Head over to www.thredapps.io and click Developer Portal. Register for a Thred account and agree to the Terms of Service.
Developers can choose to set an installation fee on their apps. Installation fees are uniform across the different networks the app supports. For instance, if you were to list your app for 1 ETH on Ethereum, it would cost a customer to 1 MATIC to install it on Polygon.
If you would like to set different fees per. network, consider turning your app into 2 different applications. One for ETH, and one for MATIC.