Started a Upper/Lower routine at the gym 4 times a week and loses the ability to perform pull-ups

Hi everyone, I recently started to go to the gym for the past 2 months. Previously, I often trained calisthenics such as pull up and push up. Now, since I often go to the gym, I replaced pull-up with other back exercises such as rowing. Today, I decided to test my strength on pull-up but I can't even do a single one. How can I regain those strength while keeping my gym routine? I missed the ability to perform pull-up as it is one of the longest excercise for me to master since I started my workout journey.