To un-vault a document, go to vaults

Then select the vault with the document you wish to un-vault. Click on "_ items in vault".

This will take you to a search with these items in a list. Press the three dots next to the document you wish to un-vault  and "Manage Vault".

To un-vault a document change the vault to "None" and "Save". Or you can choose a different vault to move the document into.