Statuses in the past can only be changed or removed by Admins.
Use the search filters on the Calendar page to find the status you need to remove.
Hover your cursor over the status and select the More (...) button.
Choose Edit and select Remove status.
If you don't have Admin access and need to have a previous status changed or removed, contact one of your Pingboard Admins for help. You can find your Admins listed at the bottom of the Help page in your Pingboard account.