iMessage not working on iMac after macOS 15.6 update

Since I updated to OS 15.6 on my iMac my iMessages app will not work. I have looked on line for help and it wants me to go to systems settings/apps/imessage. I can't find the apps setting on my mac. HELP!

[Re-Titled by Moderator]

Original Title: iMessage not working after os 15.6 update!