HTTP ERROR 500

Hello,
I’m using one press plus theme, and since yesterday I can’t access my website or my admin dashboard, I get this HTTP ERROR 500. I did try to fix it by creating a new .htaccess file, deactivating plugins, I think the problem might be with PHP memory, the site went down after I added something in function.php, I tried to increase my php memory but it didn’t work. I need some direction in how to fix it

Thank you for your help!