Welcome BobLin to the Newmar forum & irv2.
I would reset jacks and level the coach than try to operate just that one slide.
Make sure everything around slide is clean and no binding.
Have coach shore line plugged in or have engine running, you may hear the alarm, open and close slide a few times it may realign with in the track rails.
Newmar Slide out Systems
There is more info in the Quick Tips Link.