You can certainly add an optional upcharge giving your attendees the ability to cover the credit card fees within the tickets you created for your event.
Within the ticket that you created, scroll down to the Options section, and select Add Option. From there you can select the Single Option type to insert a Yes or No question, "Would you like to cover the credit card fees?" and change the upcharge associated with the Yes response. Please refer to the screenshots below.
Please reach out to our Customer Success team by emailing firstname.lastname@example.org or clicking on the blue support button in the manager portal