Here is my basic version:
Find users with last login date older than 3months, and currently having 1 of 2 relevant access levels:

Downgrade these users access:

Comments:
it's very basic scenario, for me it wouldn't be worth keeping it as a separate one, I would rather add these 2 modules to some other scenario that runs on regular basis OR build this one out to handle some other tasks as well. Assuming it would run on regular intervals.
Good luck!