What is the way to get rid of the recurring obsessive thoughts about ritual purity (tahara) and prayer that lead to repeating the prayer multiple times and prevent performing Umrah?

The condition you are experiencing is from waswas (whispering doubts), and its cure is to turn away from it and ignore it. Perform your ablution and pray normally, without paying attention to these whisperings, and do not repeat the prayer after you have finished it. If you are certain that urine has exited you, then your ruling is that of a person with incontinence ( سلس ), and you should perform ablution for each prayer after its time has begun. Pray as much as you wish with this ablution until the time for that prayer expires. What exits from you during prayer will not harm you. There is no harm upon you in performing Umrah and other good deeds if you apply these rulings and ignore the waswas. You may consult a trustworthy psychiatrist.