Let them roam freely in the tank. Snails are incredible helpers at breaking down organics into miniscule bits that the bacteia can then more easily deal with. And snails get into every nook and cranny doing this. Plus they do eat algae from plant leaves, minimally, but they help.
Photos below are of the Malaysian Livebearing (or Trumpet) snail (group on the glass), common pond snail, and ramshorn snail (shell circular like the horn of a ram). The colour and patterning can vary, but the shell shape is distinctinve for all three.