You can use this method if you don’t have a dehydrator or a fryer.

Preheat the oven to 200 degrees Fahrenheit (or 93 degrees Celsius) or lower.
On a baking sheet, place the marshmallows on a single layer.
Pop the marshmallows into the oven.
Toss every 20 minutes and bake until the marshmallows are completely dry. This should take about 2 hours.
Once done, allow the mallows to cool and remove them from the oven once cool.
Store in an airtight container or vacuum seal for longer storage.