You can register on existing cryptocurrency exchanges because they are already widely available, and then you just need to send your coins to the address of the corresponding coins on the exchange and sell them. I was wondering, when you bought a few years ago how did you buy because I thought it would be weird if you didn't know how to sell it. Btw, I really regret selling Dogecoin too fast yesterday, because if I sell it at the right time then I'll be a millionaire in no time.