How to change signer on a document sent for signature by an Echosign user who has left?

I have a user who has left the company. He has shared his account so the documents are visible to other team members.

The signer/recipient is no longer valid so we would like to change the signer.

The option to change the signer is not available under Manage as the document is 'owned' by the left user (just shared).

How can I gain 'ownership' of these documents so that the signer can be changed (or worst case, the document cancelled and re-sent)?

There does not appear to be an administrator way to view or take ownership of documents to enable their maintenance from another account?

I tried changing groups to match that of the document sender but could not see these documents as an admin either.

Advice and help would be much appreciated.