The website can't open, instead it downloads index.php

I just changed the lsphp74 handler script to lsphp83. And the result actually made the website unable to open. Instead download index.php. And when return it to the original settings, it still doesn't change anything. Still downloading index.php. Can anyone help me?

System: ubuntu 18.04server: openlitespeedweb: wordpress

RegardHarry

I already try reverse back to lsphp74 without change anything, but still doesn't work.