What token do you have?

you should visit

https://coinmarketcap.com/

search for the token you have and click on it.

on that page select the markets tab and find the markets and trading pairs for that token.

Then you will have to create an account at the crypto exchange market and trade the token for BTC.

Alternatively it may be possible to exchange it simply by using a crypto swapping service like shapeshift or changelly.

I have ATHENA and I can't search it here: https://coinmarketcap.com/