On Desktop / Mac / Web app
Step 1: Open game preview screen
Step 2: Below the preview section, you will find a download button, tap on download button and it will copy that game into your game list.
On Mobile app
Step 1: Open a game summary screen.
Step 2: Tap on the three dot(…) button, it will expand different options.
Step 3: Tap on the download button to copy the game into your game list.