Tried it again to make sure I was doing it in the correct folder and I get the same result using raspbianOS. I also just tried it again using a fresh install of repetier server instead of raspbianOS and get the same result.
The first two commands run with no problem
pi@RepetierServer:~ $ chmod 755 Repetier-Server\ Monitor-1.4.7-armv7l.AppImage
pi@RepetierServer:~ $ export DISPLAY=:0
However upon running:
pi@RepetierServer:~ $ ./Repetier-Server\ Monitor-1.4.7-armv7l.AppImage
raspbianOS gives me the error:
cannot execute: required file not found
and repetier server gives the error:
./Repetier-Server Monitor-1.4.7-arm7l.AppImage: line 1: File: command not found