Pull-ups on the horizontal bar for some seem to be something completely unthinkable. However, it is much more difficult to do it by force on both hands. But you can learn not only pull-ups, but this exit can be done without the help of an instructor.
If you have weak arm muscles, start with push-ups. They are much easier to do than even pull-ups. These exercises should be done in 3 sets at least. Alternate push-ups with resistance bands or dumbbells.
Are the push-ups going well and free already? Move on to pull-ups. Do these exercises every 2 days. Pull up as many times as possible and take a break.
When you can calmly do 10 pull-ups in one approach, the next exercise for you will be going to one arm. Grab the bar with one hand at a 90-degree angle - make a so-called "flag" - and try to straighten it. You need to train in this way both hands alternately. Also, start pulling up from your chest. And only after that you can try to reach two at the same time.