Q: how to add a contact to an existing group on ipad

Hi  lizfromdelta,

After reviewing your post, It sounds like you want to add a contact to a group. I would recommend you read this article, it may be able to help troubleshoot the issue. 

Send a group message with your iPhone, iPad, or iPod touch - Apple Support

To add a person to a group message, tap Details, then tap Add Contact.

Cheers