Can you make adjustments to an extended stay?

I have a client who booked with me through Saturday-Thursday but now wants to extend the stay until Saturday. He wants 3 visits total (2 on Friday, 1 on Saturday) but Rover only lets you book a set amount of visits per day. How do I customize this so he's not being overcharged- ie charged for 4 visits (2 each day) instead of 3?