Want to change user P from standard to admin but system keeps prompting for password for user S

I made the change in user P somewhat impulsively, from admin to standard user,and now I want to change it back, at least temporally. However, when I access user accounts or system recovery, I always get the prompt for user S, a seldom used account on my system. I have tried a bunch of possible passwords for user S but no luck.

How should I proceed?

From any admin account you can temporarily activate the built-in hidden administrator account to change user P account from standard to administrator account.

option 1 here. If you do not have access to an account with administrative priviledges you can enable the hidden administrator using a windows install bood drive. option 5
Be sure to disable the hidden admnistrator account afterwards

Enable or Disable Elevated Administrator account in Windows 10