At what stage do you want to import CSV file, the App design phase or the delivery phase?
In the App design phase, you only need to Save-As the CSV file as an Excel file, and you'll be able to save it to OneDrive to connect to it from PowerApps, and/or you may import it as static data. (Please remember that we would need you to configure the range as a table to ensure it is available to PowerApps.)
However in the delivery phase, PowerApps only supports to import the data that exported from anther app now. For more information: Import and Export.