I registered a custom post type “job” to create job board site. Without plugin, how can I make the posts auto change status to pending after 90 days? I am new in wordpress & php, I tried some solutions found on the internet, but not working.

Sorry that I don’t really good in php, I can’t write code myself. For testing, do these solutions need to wait for 1 days if I change the code expired 1 day? Cos I paste the code in my functions.php and nothing happened.

Tried Solutions:
Code to auto expire posts after 30 days
Automatically move pending posts after 30 days and, update the post date, when users update the posts
Set post to draft after set period based on post_modified date
Posts to expire (deleted) after a date