Natural way to kill snails in the garden?

There is a poison for snails called Sluggo it is for Organic Gardens its made with Iron Phosphate

apply food grade diatomaceous earth

beer in a shallow bowl. They crawl in and drown. What a way to go.

Sparkle them with salt.

sprinkle!!

To protect a plant from snails, dust its leaves with diatomaceous earth or sprinkle the material over the ground around vulnerable plants in a protective circle.

salt

Crushed eggshells, sand or diatomaceous earth sprinkled around plants that the garden snails seem to prefer will deter and eventually kill these pests. Set out traps – A common snail trap is the beer pan. Simply fill a shallow pan with beer and leave it out overnight.

Here's a post that might help https://chascrazycreations.com/keep-pests-out-of-your-garden/