The crew is facing a situation, in which, the altimeters indicate different altitude (the port and starboard ones - cpt´s and FO´s). Is there any procedure to perform an IFR landing? If we consider a light aircraft, what the crew will do?
Since you describe a captain and FO, I'm going to assume that you are asking about a larger aircraft, like say an airliner or business jet.
Part of the certification of these types of aircraft require them to have a third (standby) altimeter in addition to the two primary altimeters.
When there is a discrepancy, the typical procedure (keep in mind that a pilot should always follow the manufacturers checklist in these situations) is to cross-check the three altimeters and find the two that agree so that the bad one is then excluded.