[Halloway]

If I try to install a nightly build from http://mirrors.kodi.tv/tools/kore/nightlies/ I can download the file but when I come to install it, my Android 7 phone throws an error message: "App not installed. The package appears to be corrupt."

Is there anything I can do to fix this?

[syncd]

Shouldn't happen. Have you tried a release build (the latest is the same as the nightly) http://mirrors.kodi.tv/tools/kore/releases/

Also, try uninstalling Kore first, or use adb install -r

[Halloway]

Thanks for your reply. You mention using adb - I've just been downloading the install file from Chrome on my phone. Is this the correct method or should I be connecting the phone to my PC and using adb?

[syncd]

If you were able to install it just by downloading it in chrome it should still be working (nothing changed in that regard afaik). I just use adb for installing. 

Try uninstalling Kore first then.