Apple released a temporary fix for iMessage issue which cause instantly crash Iphone and difficulties to access the messages app.
A bug in Apple’s iOS allows anyone who sends an iPhone a specific series of unicode characters(a string of English ,Arabic&Japanese characters) cause the receiving iPhone immediately crash.
How to get access to the Messages app ;
1. Ask Siri to “read unread messages.”
2. Use Siri to reply to the malicious message. After you reply, you’ll be able to open Messages again.
3. In Messages, swipe left to delete the entire thread. Or tap and hold the malicious message, tap More, and delete the message from the thread.