Difficulty in setting up letsencrypt SSL

I have installed OpenliteSpeed through one-click install. But setting up letsencrypt SSL is big probelm. I am still not able to setup it properly. All the instruction are old and not working.

Can someone please point me toward the right Guide or webpage that clearly outline the setup of letsencrypt SSL in OpenliteSpeed.

I have spent two days to figure it out but not succeed.

Your step by step guidance is highly appreciated.
I'm getting following error when installing Letsencrypt following your steps:

WARNING: couldn't find Python 2.7+ to check for updates.
./certbot-auto: 919: ./certbot-auto: python: not found
How to solve this?