Is your lens with 10 aperture blades or 6?
If it's 10 you might be able to do it yourself, the ones with 6 seem to have much more difficult construction.
I managed to do the exact same thing when I got my lens - tilted the lens while lubricating the aperture ring and then wondering what the weird rattling sound was... my first and only aperture reassembly job, I think I spent a few hours over multiple days until I got it back together.
Once you get frustrated, put it down and come back a bit later.
You can see the basic process used in this video - https://www.youtube.com/watch?v=3_lRB6vXbP8
Expect it to go a lot worse though if this is your first try. Oh, and note that the pins on blades are not the same on both sides - on is centered and one is offset. So make sure you are inserting them the correct way