I'd definitely take the opportunity to make sure the BIOS is up to date (just to be sure you're running one that supports the newer CPU), or just default everything if you're already on the current version before pulling the 5600G and dropping the new one in. Then after you've confirmed the board recognizes the 5700X3D it's just a matter of changing your settings back and dialing in the memory timings.
I know it's tedious, and probably not strictly necessary, but I figure it's better to start off with a clean slate whenever you swap out a CPU or reconfigure your memory, just so something you didn't think about doesn't come back to bite you later on.
I usually just go through all the BIOS screens where I've made changes and take photos with my phone, then use those as cheat sheets to refer back to.
I'd like to think that $3K asking price means the shop owner is in on the joke, too.