The recipient of an email notification with a document link can forward the email to another person to sign. To maintain the integrity of the audit log signers should use the "Change Signer" link within the email.
Admin Users can add or remove this option. Go to Admin > Signer experience > Email options and tick the option 'Signer emails include link to change/forward to another signer'. This setting is turned on by default.
If a signer clicks the Change Signer link a browser window pops up where the person can enter a new name and email.
It will look like this:
You can amend a signers' details yourself too, read how to change a signer's email or name.