I have had to do this.  The easiest way is to open the 32 bit database in the 64 bit Access environment.  Then go into a code window and compile the code.  It will start bowing up where you have not put the ptrsafe code, which is typically on functions.  Once you compile with no errors, then you are most likely done fixing the broken code.  It will then work in both 32 bit and 64 bit, but it might depend on what the code is doing as every database is different...