Leave the pump together, and yes, leave the regulator side (the float bowl side) apart.
Hook your pop-off tool to the fuel input, and plug the return.
Put a couple drops of oil on the needle and seat, and start feeding it pressure. You should get a clean "Pop" at what ever pressure you are looking for. If it starts to hiss at you... then the needle and seat may need to be replaced, or, you didn't get oil on the tip of the needle.
This process will spray oil when it pops... so watch your eyes.
To retest, you will need to re apply oil to the needle.