How to scale rubi Normal mode

I am trying to get a slag eviceration Rubi, if but it’s only level 19 and I’m about to beat normal mode. How do I scale it to around level 23 or 24

You have to wait to accept the mission until the map/game has scaled up to the level you want. If you already accepted the mission in your current mode, you’ve already locked the level you can get. And since it’s a mission reward, you’ll either have to wait until TVHM, or grab one using a different character (but wait to take the mission).