Please help me with this moving users from 1 grp to another

I have email validation and moderation queue on for new user registration.

I want to move users in grp "waiting email validation" where location=XYZ to another group ID Y

That is, something like this:

update user set usergroupid=X where location=XYZ AND usergroupid=Y;

Or where timezone=-8

The reason for the above ie I want only users of specific locations from a specific groupid Y is that I want it because of particular reason.

and also I do not want all the users awaiting email validation to be moved to registered as we have a major problem with a few trolls who just keep registering duplicate (10-15!!) accounts on and on and on again....

The prob is I am not a mySQL expert and I do not know how vB moving groups works with such queries