If you don't want to crack the colony apart, maybe do something to temporarily anger the zoa so they close up? That'd make it easier to get at the aiptasia. Idk, like just take it out of the water for a minute or something.
Also, scraping or breaking them can spread it by pedal laceration so be careful. Also, angry zoa can squirt and some have palytoxin so be careful if you take it out of the water. Lol just be careful I guess.