Hi, mate. Itch.io puts the apk inside of the downloaded zip file, so you'll need to extract it rather than rename. The file should be named 'com.domain.rewind-3.3.6-international.apk' (all versions should have the same name aside from the version number). Let me know if it's still giving you an error (other than the usual 'are you sure you want to install from an unknown source' message... I can't do anything about that one unless Google starts allowing porn into the play store).