Dual boot option disappeared after resetting one of the windows 11 installations

I have a PC with a 500 GB SSD M2, with two partitions of 250 GB and one HD disk of 1,8 TB. I have installed windows 11 on both SSD partitions (dual boot), and use one for office work, and one mainly for Microsoft Flight Simulator (MFS).
MFS ran nicely for some months, but in the last few weeks, it refuses to start. Repeated attempts to update MFS only result in an error message saying "Something went wrong". Windows 11 is fully updated. I uninstalled MFS, but when I try to reinstall it, I get the same error message.
I then decided to make a complete reset of the corresponding Windows installation, leaving the other untouched. That seemed to work ok, but when I restart the PC the dual boot option is gone. My problem is: How do I get back the possibility to dual boot my system?

Your other Windows partition should have a drive letter, let's say it is E:. In a command prompt with admin privileges the command would be:

bcdboot E:\Windows /d /addlast

Change the drive letter to whatever matches yours.

Thanks for responding. I tried your suggestion but mixed up the partitions, and was left without access to any of the Windows installations. Bummer. Luckily, I remembered that I had to enable PTT the first time I installed Windows 11. Checked BIOS, and secure boot was not enabled. I reenabled it, and suddenly I had dual boot back. Great relief.