How to reset my iMessage on iPhone?

How can I reset just the texting app, I sent a huge text of just emoji symbols (HUGE HUGE text) and it froze and doesn't open anymore, can I reset just the texting app without resetting everything else on my phone? Could I call AT&T and have them reset it for me? Cuz I don't want to reset my phone

Have you tried holding down the power button (top right) and the Home button for a few seconds? The phone will turn off and restart but won't delete any of your data or anything. That usually fixes any problems I'm having!

I can't get in my iMessage for I can text