Hi,

Thank you for reaching out to the DocuSign Community.

For completed envelopes, I'm afraid that you won't be able to modify them.

 What I can suggest is to create a copy of the envelope and send it once more ensuring that the additional recipient is added, or you can opt to use the Forward feature to create a copy that you can send to the new recipients as is, or add new documents and fields as needed.

Here are some resources you might find useful:

Add Recipients

Forward a Completed Envelope

Copy Envelopes

 If you believe that you need further assistance, or require the assistance of a live agent, you can always create a Support Case to have a Support agent work with you. 

https://support.docusign.com/s/contactSupport

If you are not able to open a  Customer Support case via the above link, you can scroll down to More Support Options and select "I can't reset my password or don't have an account." you will have the option of filling out the form or calling Support.

Please click "Select as Best" below if you found the answer to be a valid solution to your issue. 

Thank you for using DocuSign, we hope you have a wonderful rest of your day!

Best regards,

Rebeca | DocuSign Community Moderator