From the participant list, click Edit registration to open the editor with all the participant's data.
What you can edit
The registration's form data (name, ID, club, custom fields…)
The bib (also editable directly from the table)
The registration status through the list's actions (complete, cancel, set to pending review)
Changes with a financial effect
If the participant switches to a fee with a different price, consider charging or refunding the difference. Fee changes by the participant themselves (and the automatic charge of the difference) are controlled under Settings → My Registration
Refunds are processed with Refund amount (more details)
After editing
If the registration is synced with Copernico, sync it again so the timing system gets the updated data
The participant can see their updated data in their My Registration portal
Participants can edit their own registration if you allow it in the My Registration configuration.