There is no setup. No settings to fiddle with. Just edit.
Just open the bin containing PAL footage in your NTSC project. When you cut it into an NTSC timeline, Avid takes care of the rest using what it calls Motion Adapters.
This is an FCP forum so we should not delve too deeply into Avid tech support here.
Post in the Avid forum for further help…where you should get lots of answers.