You can take the following actions to ask for a refund on a United Airlines cancellation:

• Enter the United Airlines refund policy area on the official website.
• You can use this link to complete the refund form.
• When you click the link, a login prompt will appear. You have the option to sign into your Mileage account or continue as a guest.
• After that, fill out the appropriate fields with the information requested about you.
• The next step is to include your travel in the form.
• In the following option, provide some extra notes and reference attachments for the refund request.
• After that, submit the form and wait for the United Airlines refund department's email answer.

Read more : Hawaiian Airlines refund policy