Dear friends;
Does anyone know where I can set the forward or backward parameter in MRP.

There was never any forward or backward concept in MRP. If you're talking about forward or backward levelling in RCCP, then it is in Constraint Planning parameters session in BaanERP (I think there's a similar screen in BaanIV, because BaanIV's RCCP can also perform forward or backward levelling)

Rgds,
Paul