You don't necessarily need to SWITCH. It's always good to have a varied diet.
I'm assuming your leo has never had mealworms before, and is probably not used to eating out of a dish? I would start by first dusting whatever amount of mealies you are going to feed them. Take one or two, and plop it in front of the leo. If it's moving enough, the gecko will go after it. It's obviously used to hunting down and eating crickets, so a non-moving mealie will be of little interest! Superworms are a lot more active than mealies, and a few of my geckos will not touch mealies, but go nuts over supers. Some geckos are just picky!
Chances are, they will find the dish you leave in the tank. All mine have, after a bit of exploring If not, you can guide them to it while you're adding mealies.