You shouldn't buy coins because of FOMO, if you missed the train - you missed the train. There is no point in running to catch it.
It is first rule of trading.
Which coin did you buy at ATH? You can stoploss or hold to new ATH (if it is a good coin) 
It doesn't matter which one, you don't buy coins at ATH It is first rule of trading.
Maybe you need to be patient hold the coin for a long time in order to generate a profit. don't get too panicked about the issue price of the coin because if you panic thus will lose out.
I don't think OP has much choice, either he will hold for long time and wait to recover or he can sell and lose money.