How do you delete conversations with dog sitters who cannot sit when I need them?

We had a dog sitter lined up, but she has cancelled 5 days before we need to be away. I have contacted other dog sitters and gotten "not available" responses from all responders so far. I have reached the max. number of conversations I can have on Rover, but I am in a BIG time crunch. How can I delete the conversations of "no" responders so that I can continue contacting potential house sitters on Rover?