Depending on what country you're in, but personally I'd go with Binance[1]. Create an account, send the BCH over, and sell it for BTC.

And of course, make sure to withdraw the BTC after and store it on a reputable wallet.

[General] Bitcoin Wallets - Which, what, why?: https://bitcointalk.org/index.php?topic=1631151.0

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[1] https://binance.com/