All markups can be edited, for that click on "Edit Markup" in the toolbar at the top of a sheet.
Any parameter can be changed or deleted, also text boxes can be rotated.
Click "Done" to save changes and all the users will see the updated markup.
Previous versions of the issue’s markup are available in issue’s Chat, click on the message to see the previous version. To roll back or work on the previous version, click on "Edit markup".