If your doors are sturdy, make a knot in a towel, hang it over the door and close it. Use that to do pullups. I used to do this a lot during traveling.

You can also do inverted rows under a table by holding on to an edge (not comfortable, but works).

You could invest into a dumbbell and/or resistance bands and do row variations. Or a TRX for inverted rows.

Or go to a park or anywhere else where you can hang onto to do your pullups.