Please see this guide in the documentation on how to go about compatibility testing and how to modify existing plugins to work with OctoPrint when running under Python 3.
What is the problem?
What did you already try to solve it?
Unable to do so
serial.log or output on terminal tab at a minimum, browser error console if UI issue ... no logs, no support!)
Additional information about your setup (OctoPrint version, OctoPi version, printer, firmware, browser, operating system, ... as much data as possible)