I have adhd and haven’t been able to complete programs in college , not knowing

I have adhd and haven’t been able to complete programs in college , not knowing I had adhd and it just made it so frustrating for me I was out on probabton. I want a letter written stating that I have ADHD and that I will do better in school but that’s whu and that is why I haven’t been struggling in school but want to be given a chance because I have potential and that time limits given to me just cause my anxiety to go up and cause me stress and just makes me frustrate that I can’t hand things on time or focus the way I want to