It'll fall off on its own when it's full
but if it was my cat I'd want it off sooner than that. If it's a feral the stress of catching it would probably be MUCH worse than any harm done by the tick - there is a possibility of their transmitting disease but the damage is surely already done, yanking it off now couldn't help that.
If the moggy is a regular visitor, you could try and frontline him/her...