i try this :

1. Log into your PostgresSQL database
2. Run this to find the User ID of your admin user: select id,login from res_users;
3. Run this to give you access back to the settings: Insert into res_groups_users_rel values (the_id_found_in_step_2, 2);

But it s not working for me, the table res_groups_users_rel have 2 columns gid and uid, i guess uid is 1 so i invert values for the query n°3 : Insert into res_groups_users_rel values (2, 1); => "settings" not appear

Edit (can not post a new answer) : Good Work it works !!! Thank you

 Can you please try to restart odoo server with --update=all 

I think you changed access rights of admin. You need to re assign access rights to admin user by query..