From the official Frontier website, locate the local office's hotline number and dial it to get in touch. You may hire a team member to help you through the cancellation process in real time. He can assist you with any further flight-related problems you may have in addition to that. Additionally, if you give us a call, we'll help you cancel. Additionally, we make certain that you receive your money back free of any complications and after any unauthorised cancellation fees have been subtracted.

See: https://www.airlinesadviser.com/flights-cancellation/frontier-airlines-cancellation-policy/