Try reaching in. If you can do it, great!
I couldnt get my hand in there to do anything. Just not flexible enough I guess. But, pull the battery tray and remove maybe 6 bolts and the inner fender comes out much easier than I thought it would. Get it up on jack stands, remove the wheel, then the inner fender. It comes out the bottom toward the outside. Went back in easy too, and theres no issue with panel (fender-door-hood) alignment like youd have if you pulled the outer fender.
If you do that, might be a good time to change the heater core too.

PS.  I think the manual suggests undoing the bottom rear of the inner fender, then propping it open with a 2x4 so you can reach in from the bottom - at least thats the procedure for changing the heater core