To assign a witness to a document, follow these instructions:
review the document that was sent to you, sign at the bottom of the page and click on Approve & Sign;
if the document requires a witness, a small form titled Share with witness will pop up;
fill the form on behalf of the witness and click Submit; the witness will be able to edit this information if necessary;
the witness will be sent an email with instructions; you can also share the link that pops up after submitting;
when clicking on the link shared or received via email, the witness will be asked to check the information and sign the document.