Setting an extender for default wifi

I have a Telstra 4G modem and three TP-Link extenders set up. Now I would like to set the large 650 extender as the default broadband source but am now unsure of how to do this so before I go ahead and wreck the system I would appreciate if a forum member could give me some guidance.
The actual situation is when I boot the computer in the morning the broadband source sets to the slow modem and not the faster extender - a good 5Ghz signal as opposed to the modem which shows up as 2.4Ghz.
I had a dig around on the net but could not find any reasonably simple way to fix the issue.
See pic for the different settings.

This might help:

Thanks Navy I think I have it set up for the extender now if not then it will not be a big deal - just annoying.

NavyLCDR said:

This might help:

How to change Wi-Fi network connections priority order on Windows 10

If your PC keeps connecting to the wrong Wi-Fi network automatically, in this guide, we'll show you the steps to change their priority to always try to connect to the preferred network first.

www.windowscentral.com

Click to expand...

Reading the beginning of that article I have to say making those settings didn't help. No matter what I did my desktop would occasionally disconnect from my Comcast router and connect to my Rock Space repeater. No matter how many times I selected to not connect automatically it still would happen. Even choosing the forget network option didn't help. The repeater was further away from my computer than the Comcast router and always had a weaker signal so I know it wasn't connecting because of a stronger signal. I finally just gave up and when I noticed my Wi-Fi was running slow I would reconnect back to the Comcast router. About a month ago my Rock Space repeater broke when it feel on the floor. I replaced it with a Asnrc repeater and so far my desktop hasn't tried to connect to it. As a bonus the Wi-Fi speed and signal strength is much better on my computer I have setup in my shed.

Yes I get what you are saying winuser mate my issue is almost identical to yours except that the main ISP 's modem has a much weaker signal than my TP-Link extenders. The modem being picked up by my laptop being 2.4Ghz from the modem and 5Ghz from the extender. The thing being that the download speed is very much affected by my laptop being in a solid brick part of the house as apart from the modem being situated quite a distance from the laptop in a wooden constructed top part of the house (because the house being over 120years old is built in a composite manner for that time era). The problem is that I keep the extender connected during the day and on boot up the next morning the wifi automatically sets the modem as the signal source and I just have tried a few fixes with no luck. I even tried that command line option to fix it but it came back as command not found. So I shall just have to keep changing it every day when I boot up eh??

Well mate I am trying another tack and that is to set the extender as an automatically connect and set the modem source to forget by right clicking on the sources when I pull up the list via the wifi icon on the taskbar and setting them that way as the command prompt method was driving me nuts so we shall see tomorrow eh?

Can you not connect the needed router through an ethernet cable ?
Windows always gives first priority to ethernet ?
Regards

Thanks for your reply cineman mate the modem is situated some distance from the laptop and it is in a room that is constructed with 10" thick brickwork walls that block any 5Ghz signals hence I am using three TP-Link extenders that can get a better 5Ghz signal that gives me a far better download and upload result in my speed test.
As for connecting with an ethernet cable that is really not a reasonable setup because of the distance between the rooms that accommodate the modem and my laptop. Hence it would require having a very long cable from the modem to the laptop or running a cable through the roof spaces and down the wall and then onto the laptop. The latter option would be very expensive to have installed as my house is well over a hundred years old.
So as I mentioned before the extender I have set via that icon on the taskbar to be the default source on boot up, and will have to wait and see what happens tomorrow when I boot up.

A powerline network adaptor may be the best solution.

Thanks cerebus mate I have never heard of that before an will have a look into it and actually the problem I started this thread with I have just about resolved as the machine always boots to the Wi-Fi connection that is needed to get my full 50mbs download. The problem overall is that out here in rural Australia the broadband is absolutely pathetic and the only folks who have say 100mbs and above are those who live in the major cities. It is aa sore point with us country dwellers and there seems to be no hope in the near future for us t get anything else than what we have right now.