Initial Seed for LFSR in PSpice
I would use the ".ic" (initial condition) directive.

Name any node (or find a node name) and then add the directive .ic V(nodename)=required voltageV

In this case, SPICE may struggle without an initial condition for both XOR inputs. I would probably set initial conditions for every flip-flop in this situation.

Update: where to add ic directive.

I would put the directive at the top level node to start with.