What should I do?

WARNING: this may be a sensitive topic for some.

I believe that I was sexually assaulted but I don't know what to do, to tell. I've been sitting on this for over a year now.

So let me give you a bit of a backstory...
It was wireless 2019 and I was just split up from my friend. We had travelled hours to get to this festival and we were near the front in the beginning. Eventually the crowds started getting wilder and around the time Gunna came on I had lost my friend. I saw this girl who was also in the same position I was so we decided to stick together and move a bit further to the back. It wasn't until then I became painfully aware of my surroundings after a guy came and pressed himself behind me. His hands started roaming everywhere, my backside, my front. I literally couldn't do anything but freeze. I was literally planted on the floor, and so many people were giving us weird looks probably thinking we were a couple. This literally went on for the rest of Gunna's set, and i told my friend afterwards but brushed it off as a joke.