Thanks for replying! I tried to look into Security & Privacy pane, but there is no button there for me to press. Also the alert shown with the error message isn't the same error shown when an app is from an unidentified developer.
I dug into the mac logs and found this, hope it helps!
Apr 21 19:48:57 MacBook-Pro com.apple.xpc.launchd[1] (com.apple.xpc.launchd.oneshot.0x100004cf.The Messenger Assist[73231]): Could not find and/or execute program specified by service: 13: Permission denied: /private/var/folders/n4/qhwt0jjx6dq69pkt47vhl5_40000gn/T/AppTranslocation/C77E4054-70BB-4352-938B-C358FF4DA98C/d/TheMessengerAssist_MacOSX.app/Contents/MacOS/The Messenger Assist
Apr 21 19:48:57 MacBook-Pro com.apple.xpc.launchd[1] (com.apple.xpc.launchd.oneshot.0x100004cf.The Messenger Assist[73231]): Service exited with abnormal code: 78