I cannot name a group for a group text or add someone to the group. Please help me with this.

I created a group text with 11 people on it. I forgot to enter 2 people. In the info area, which shows me the name of everyone on my text, I should have a place to enter a group name, (which I don't have) and the ability to add or delete someone from that group (which I don't have). Anyone know what's going on and how I can fix it?