I think you're confusing concepts.
What you can modify is the percentage you share with Itch from your sales. This is 10% by default and can be modified in settings. However, this 10% only applies when someone buys something. For example, if you sell something for $10, $1 of those $10 will go to Itch.
EDIT: My mistake, you're just talking about the maintenance charge.
The other thing is a maintenance fee charged when you have unclaimed money on Itch for more than a year. This maintenance fee is NOT configurable as it is an administrative fee, and to avoid it, you simply have to make sure to withdraw your money at least once a year.
EDIT:
I don't think there's an area that shows you exactly what you're asking, but you could try to figure it out by reviewing your payment and withdrawal history on the dashboard.