I'm not sure if the 2002 Avalon has a cabin air filter, but if there is one,
it is probably behind the glove compartment.  Open the glove compartment and
squeeze the back left and right corners so that the glove compartment opens
completely.  The cabin air filter should be visible behind the glove box.

The filter comes with instructions.  Also check your car manual.  On my 2001
it was under the glovebox.

OOPS -  We had an 02 Avalon and the instructions were there like Art says.
BUT, in ours it required taking out about a half a dozen screws around the
glove box and a small bolt on the right side - then slip glove box out box
out.  It isn't as bad as it sounds - actual filter replacement might have
been 2 or 3 minutes!.

We had a 98 Avalon, have an 02 Highlander and an 05 Avalon and all of them
are essentially like Ray says.

FWIW, I just changed them and they are each $29.95 at dealer - much cheaper
on line but the 05 hard to find.

Ron in Ca