To remove a Form from your dashboard the workflow owner (1) first needs to uncheck "Publish Form on Dashboard" from the sidebar menu.
Then remove the spreadsheet from the Dashboard (2)
If a Google Form has been permanently deleted from Drive but is still showing on your Dashboard you simply need to remove the spreadsheet from the Dashboard. Once the spreadsheet is removed the permanently deleted Form will also be removed from the Dashboard.
My Form is no longer linked to a spreadsheet
If a Form on the Dashboard is no longer linked to a spreadsheet please proceed as follows:
1. Search the spreadsheet name in your Drive, as it appears on the Dashboard
2. Start Form Workflow Plus on this spreadsheet
3. Click Create on the Set up tab
4. Once a Form is linked uncheck Publish Form on Dashboard
5. Refresh the Dashboard https://app.formworkflowplus.com/forms.
Requesters will no longer be able to access the Form from their Dashboard