After 4 hours has passed, without removing any of the starter, feed it ½ cup warm water, 1/3 cup sugar, and 2 Tablespoons of potato flakes.
Let it remain on the counter for 12–24 hours.
During this time, you should start to notice more bubbles, a little foam, and possibly some movement that can be described looking like a lava lamp. If it still looks sleepy, don’t panic.
Many people report that after a second day (or even a few days), their starter finally perks up in a big way.
If your starter has been in the fridge for a while, give it time. It may take a couple of days to bounce back, especially if it’s been neglected for a few weeks. Patience and consistency really do pay off.