Best tool is a hole punch - https://www.amazon.com/EK-tools-Circle-Punch-1-Inch/dp/B00C90WM14/ref=sr_1_5
Can't remember the exact size but I believe the round targets are a 1" circle. I may have used 7/8" or another size. You should be able to pick one up locally at Michael's, Hobby Lobby, Joanne's etc.