How do you adjust the band on a rolex watch

You would have to unscrew the back (needs a special tool) and leave it open to dry..then probably have it cleaned. Only a professional watch mender can do this.
BUT Rolex watches are water resistant. It either isnt as Rolex, or you went too deep

Its time for a service.
Take it to any Rolex re-seller that offers repair or to any good timepiece service center. If its a vintage piece i would recommend sending it to Rolex, paying the extra cost to receive the watch with full Rolex repair documents and service history. The Rolex web site has information on this. Also this company does a fine job on Rolex repair. https://www.bobswatches.com/rolex-repair-service

mcdevito75 here, Most likely the manufacturers ID for that particular band.

If you don't have this ORIGINAL VALID STAMPED INTERNATIONAL ROLEX WARRANTY then your watch does not have any warranty. Just approach the dealer and ask him for ORIGINAL VALID STAMPED INTERNATIONAL ROLEX WARRANTY otherwise your watch does not have any warranty

Rolex, at one time, had a quartz (battery operated) watch. It was only manufactured in solid gold and was distinctive in style from other models. It is no longer being made. For all practical purposes, it you see a battery operated Rolex it is not genuine.

Hello

I bought one while on a buisness trip to China. I like the watch alot but the band was too big. I have a friend who's a jeweler. He fixed the band for free. It does take a special tool (which he had).

there is a little flange on the clasp that can be bent to make it snap tightly.  Most jewelers will do this service for free while you wait. 

there is a little tab on the strap that need to be bent slightly to tighten the clasp.  Most jewelers will do this for free.

Check the sides of bracelet. You will notice screw ends. Undo them with watchmakers screwdriver.
Make sure screwdrivers blade is hardened steel and in perfect condition or you will damage the screw head and will not be able to unscrew it anymore.