FAQ
How do I associate a file type with an appimage?
Try this solution https://askubuntu.com/questions/819782/how-do-i-associate-a-file-type-with-an-
Tutorial “Running LibreOffice 6.1 on al distros”
http://www.ubuntubuzz.com/2018/08/running-libreoffice-61-on-all-distros-in-appimage-format.html/
LibreOffice Appimage with icons