1. Negatives pull-ups;
2. Assisted band pull-ups for + reps;
3. Maybe start with chin-ups... your biceps will help.
And between the pull-up protocol... train to develop your back muscles... deadlifts, rdls, pulldowns, pullovers, all kind of rows, back raises, hyper deadlifts.
put a bench under the pull up station and use your legs to help you do the pull up. Eventually you will be able to do the pull ups without the assistance of your legs