Im sorry to say but the only way i have successfully removed damsels is by removing most rock and cornering them with 2 nets.
Trying to do it with one net and not removing the rock is gonna result in a very long if not impossible process and lots of stress to the fish.
Catching a damsel is one of a long list of reason why i dont recommend them. Besides clowns of course.
Trapping them is usually a fail. And catching more than one this way is extremely difficult. Trapping takes excessively more time and failure than just taking your rocks out and netting them to begin with.
Starving is can help get a damsel into a trap sometimes but it too has a high failure rate, not to mention a bit cruel and again a slight waste of time.
This is why depending on tank size and rock work etc that damsel often times become life long tank members once added. I tried trapping a yellow tail damsel for six months with a DIY acrylic trap and some fishing line. I never caught him in the trap and by the time i finally decided to tear out the rocks and net him i was so mad at the fish i was gonna have a panic attack lol. He was an ******* of a fish so i gave him to my buddy
Save your time and sanity.