Help needed to mass reset usertitles

[Mireade]

Hello,
I'm a very beginner user in mysql and phpmyadmin.

I changed the options of my board . Now the user can no longer use a custom title.
Though, all the customtitles (that were before possible) are still there.

I saw in phpmyadmin that the titles are in the field "usertitle" and that there is another field named "customtitle" that seems to have a connection with the other one.

What is the exact syntax I have to enter in phpmyadmin to reset the usertitles to the default ones ?

I believe it's an easy job but I don't want to make any mistake.

I know I have to save the whole database before everything. :-)

If someone could guide me.... (please speak to me just like I am very stupid)

Thanks
Michel