The suction cover will come off the wall fitting either by removing the screw(s) or by unthreading counter clockwise.
Once the cover is removed you can then access the wall fitting which sounds to me as if it may be broken. If you remove the wall fitting you need to put a small bead of 100% RTF silicone around the lip of the wall fitting before you thread it back into the fitting behind the tub.
Once you tighten that wall fitting up you can clean up any excess silicone mess with denatured alcohol.

Rod
U S Parts Center