I have a 2014 xterra with a heater coil issue Lyn lyall Chevy can't fix...

why can't they fix it? And why is the heat not working

The heater core on a 2014 vehicle should NOT have had any restrictions in the first place .. Furthermore the heater core is not going to cause a no heat condition - just on one side .. Without more details and hands-on testing - I would have to guess there is an issue within the baffling - inside the heater case. “Why they can’t fix it” is unknown.