I assume it's in a rubber.
It's a lot easier with two if you've never done it before
Put the rubber on the glass.
Get yourself some nice (NOT THIN) string and lay it in the channel in the rubber that's going onto the metalwork.
Sit the glass and rubber on the bottom lip and with one person holding the glass onto the bodywork on one side from the other pull the string out, slowly, and that will flip the rubber onto the metal work.
Thin string will cut into the rubber.
You might have to persuade the last few bits, don't be tempted to use a screwdriver, find something that won't puncture the rubber.