The modern way to progress to chin ups normally involves bands and eccentrics, but you can also just do partial reps (starting with the top of the movement) and gradually work on adding depth.

(This also avoids the stress on your elbows that can happen from the bottom of the rep if not controlled well.)

If you're quite far off starting with bodyweight inverted rows and working up in reps will train your arms and elbows in a very similar way from an easier position.

Anything "partial" gets a bad rep from people ego lifting with weights but it can be a legitimate way to work up to calisthenics exercises and saves fiddling around with bands