Short term storage
According to mom.com, meal worms prefer dry food, oatmeal, wheat bran, chicken mash or cornmeal. They suggest to use a 2- to 5-gallons container (7.5 to 19 litres) made of plastic with a sealing lid. Add about an inch of dry food to it. Then place a chunk of raw potato, apple, carrot or banana peel to it. Make sure to change the humid food every 1 - 2 days to prevent mold.
Pour in the worms, seal the lid and poke some small holes in to the lid, small enough to not let any worms get trough. Then place the container in a dark place at temperatures below 80 degrees Fahrenheit (about 26.7 °C *) for short-term storage.
* Other pages recommend (thegutload.com) 65 - 70 °F (18.3 - 21.1 °C)
Long term storage
Also according to mom.com, use grain instead of oatmeal or similar and don't provide any wet food. Then put it into the fridge. There's no temperature range specified on that page, but thegutload.com recommends 40 - 50 °F (4.4 - 10 °C).
The birdhouse chick recommends to pour in the grains, then the worms, then some sliced apple (remove seeds and housing before) and keep the container in a cool place (but outside of the fridge) for 24 hours. Then remove the wet food and proceed to put the container in the fridge. Otherwise, they're missing nutrients which your gecko will miss later.
According to thegutload.com the methods explained above can prolong the larvae stage from about 10 - 11 weeks to 16 - 22 weeks. That's 50 to 100 % more time to use them.
Always keep the container as dry as possible. Mealworms don't like humidity that much.
For the worms you've already put into the bowl of your gecko, just add some oatmeal for them to feed on. Although you should never put too many mealworms in the bowl at once. Geckos may eat too much, which can lead to problems (see The bearded dragon)