No, basically, take a 1/2" tap washer or something similar (Can be a
stainless steel washer) , with a small hole ( 3-6mm) in it and stick it into
the pump output flow somewhere. This is probably not a good description, but
hopefully gives a clue as to how a restrictor will work. It's very much a
"suck it and see" operation as the characteristics of the pump are unknown.
I've had to use this technique to limit the flow to one of our normal
showers after uprating the pump to 3bar and spraying the ceiling!!

Regards
Capitol