Header Image and Color

I found a dolphin theme that I really loved, but messed it up by trying to manipulate the header image and color.

Now even if I erase it and reinstall it, the dolphins are gone. Revert doesn’t seem to work, I guess because I saved.

My question is:
Is there a way to revert to the default Header Image and Color?

My blog address is https://www.acaptainsblog.com. the dolphin theme came from https://www.freestylez.co.uk/dolphins-theme/

Thanks!