You cannot edit the Finmo default document library directly - but you can easily create a new custom document with any changes you would like.
Two reasons the default document library can not be edited:
We need to be able to update the Finmo default library for all teams without accidentally over-writing any custom changes that you or your team may have made to the documents.
Smart documents default functionality requires that those default documents exist for it to work out-of-the-box.
How do I create a custom document?
See our article on creating a new custom document request (you can even duplicate an existing library document as the basis for your new document!).