If no-show, you'll still need to request a refund. In the unlikely event you have a no-show penalty in fare rule, DL hasn't been imposing them since CV19 hit. Delays in getting to agents on phone, and fact online doesn't let you cancel everything, plus lack of trained agents have meant they've just ignored it.

Best bet, if possible cancel in app/online before departure. Can be one minute, there's no cutoff.

You will need to make sure to sekect refund when doing so, otherwise it'll be left as ecredit and youll need to call in to request ecredit be refunded instead.