The server is currently in 1.15.1, I am using Multicraft as my panel.

The world is not in 1.15.1

I am being told to create a --forceUpdate parameter in Multicraft but don't understand how

If anyone get lead me there step-by-step That'd be amazing. I know Multicraft has a introduction but it doesn't explain how to do any of what it shows.
I can't create a startup parameter either, I just get a list of options in the config set up.