Changing Volunteer Selections

Hi,
I could not find this topic in the forum, and hopefully this is the correct place to post it.

Once a person volunteers for a ministry, how can they change that (remove themselves) later? When you display the profile (using the registration form) to a logged in user, the ministries section is no longer visible, and if you use the volunteer shortcode it only allows people to affirm their service for any ministry they have not previously signed up for. There ones they are already volunteered for show with a Read-Only “Already” message.
Thanks