This is a normal phenomenon. Most people have strong biceps brachii and weak back muscles, so forehand is difficult and backhand is easy. First introduce pure strength pull-ups, and then introduce skills pull-ups.

Main muscles needed for pull-ups: forearm muscle, biceps brachii, deltoid muscle, upper part of pectoral muscle and back muscle of trapezius muscle. So training for these muscles can promote more pull-ups. The following is the action of unarmed exercise, taken from the book "Fitness without Equipment":

The following six movements * * *, shoulder push-ups, bending, downward inclined push-ups, Chinese push-ups, pull-ups, forward and backward rowing. You can practice three times a day and take a day off. 10- 15 times 3-8 groups, 1 minute between groups, and 3-5 minutes between actions.

Swing pull-ups teaching video /v_show/id_XNzA5ODg4ODY4.html