I recommend you call Tech support to get the instructions on how to change the location for the synced library. I haven’t ever seen them publish the method for a Mac, just know the best way to do it on a PC (reg edit).
To contact Technical Support directly
1-800-336-4474 option 4 then 1
or
https://support.clarivate.com/Endnote/s/technicalsupport?language=en_US