My car gets under the carpet on the passenger side. Any suggestions on what is causing the problem?? (1993 buick Regal)

I had the same problem.
There is a short strip of molding under the windshield wiper cowl that came loose. It diverts the water that runs down the windshield from around the passenger compartment air filter. You might as well pick up a new air filter before you take disassemble the cowl it probably needs to be replaced anyway.

Len