Hi ananke,
Post:46521
Please see points 1, 2, 3, and 5.
You've given us insufficient information. For starters, your university, course, degree, topic, thesis, and on and on.
I suggest you browse the Internet and look for sample letters. I am sure that there must be a few. This seems like a fairly trivial task, so I would not get too upset.
Draft a letter with the pertinent details and someone will help you soon. Here in North America, it is bed time. So I won't look at your material for at least 12 hours. But I am sure that you can have your letter ready in 24-48 hours IF YOU do some homework on your own. By that, I mean assemble your basic facts and make a strong attempt at a draft.
I am sure someone will help you have your letter ready by Monday. I can help you or others will jump in.
Good luck.
MountainHiker