Just press Install anyway; you will get this message on every possible game.
Well, of course you should click the "anyway" button only if you're sure about the game and developer. I recommend downloading games only from the official source of the developers, where you can read comments about the game being okay or not.
For example, I publish my game either here on itch.io or on my Patreon. Double check the author's name and what game they produce; Google if needed. Read comments, and if you see none or comments about viruses, then obviously don't download it. But foremost, just don't use shady sites that can inject malicious code into any game of any developer. One good sign that the game is okay is if the developer chats with the people and people reply. ^^