Unfortunately, there is not a way to extend the expiration time of a document once it has become expired. Expiration dates are set at 60 days, however, with a Business or Enterprise plan, it is possible to set up your documents to auto-expire after up to 3650 days. This article explains how to set your own expiration date.
For the document to become available to the recipient again you would need to “edit” it and resend it. Editing a document turns it into a new Draft version which you can then send to the recipient. Please note, editing a document will erase all fields and signatures to protect the signer from having signed an altered document.
You can also copy the expired document and send the copy. Here is the article on duplicating documents.