Gym Cover Charge is a fee collected from customers when they enter Gyms.
Nothing is required to collect this fee, it happens automatically when customers enter the business.
Gym Cover Charge
Open your save in Big CopilotOpen in the app
From the game's own in-game help (Big Ambitions by Hovgaard Games), as shipped with the game. Big Copilot reads your save and shows your businesses, supply and staffing against it.