Backing up old messages on Mac

Hi,

I have an old MacBook Air 11" Late 2010 running High Sierra that has a lot of old messages on it that aren't on any of my other devices. I need a way to get these off of the MacBook as I am resetting it soon.

I have 50GB of iCloud which I could put them in but there is no "sync now" button anywhere in the iCloud app, and they haven't automatically synced, I am also wondering if I could put them on a usb stick somehow, but I don't believe that is possible.

Thank you