When you have stored a project on one mixer, copy it to "Local" in UC Surface (rider Import/Export). "Local" is your computer or your tablet running UC Surface. When the other mxier is connected, simply copy the project from "Local" to "Mixer".
UC_Surface_ReferenceManual_EN_04042019, quote from section 7.1.1:
"When a Project is transferred, so are all the Scenes stored within it. You can also use the Transfer buttons to transfer one preset to and from the Mixer and Local libraries. When transferring to the Mixer library, the preset will be moved to the first available Empty Location."
