But I don't know where to transfer them to exchange them to BTC.
If you are looking for an exchange to trade, check their
site. Coingecko only shows you 2 of them, but they have more than 2 on their site:
Coinsbit,
WhiteBIT,
Uniswap,
IndoEX,
HotBit,
DigiFinex,
Bazarswap,
Minereum V2 DEX. I am unaware of which one is active at the moment, just placed the links to help you. You can also find necessary information on their
Telegram channel.