Changing Gravity

I need help. I am making a game and i need it to where your player can change gravity after going through a portal. When you go through the portal, I also want to keep the jump heights, but reverse.

Can somebody help me here? This is the game I’m working on: Marble Jump Fanale
press on the 2nd lv. im trying to test it there.

In the help section, there is a game that shows how:

Thx! Helps a lot!