get your topic correctly configured in RSLinx so you are pointing to your PLC.
In iFix watch out if you have INT and you are trying to address individual bits...works much better if your analogues are DINT, and it doesnt cost you anything.
After your iFix OPC server has been installed, Create iFix tags - set source to OPC and the format of the address needs to handled carefully - it's something like:
AI:
OPCRSLinx;grpHMIPLC;AI_TAGNAME;No Access Path
DI:
OPCRSLinx;grpHMIPLC;[FIX]Input[0].10;No Access Path;;/0