Add contact to group text is not there

If you are attempting to add another user to a group text, the first thing to understand is that if you have a group message that is a mix of iOS and non-iOS devices it is an SMS/MMS and you cannot add additional users to that. If the group is all iOS devices, then you will be able to add new users. The Related Article above your post will explain those restrictions.

You're welcome. There are some other restrictions when it comes to mix messages. They are all contained in that Related Article.