From here, click the Choose File button and select the image you want to display for your Game Pass (the image must be 512 x 512 pixels and saved in either the .jpg, .gif, .png, .tga, or .bmp ...

After uploading your game, you can preview it before publishing it. Once satisfied with the game's functionality, click on the "Publish to Roblox" button to make it available to the public.