fail to use pkg install, how can i solve this problem

[pumpkins429]

i try to use command 'pkg install update' and then it came up with this error mesage
W: GPG error: https://mirrors.hit.edu.cn/termux/apt/termux-main stable InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 5A897D96E57CF20C

[sylirre]

What's your Termux and Android versions?

It looks like either you added a repo in Termux on Android 5 or your environment is messed up.

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Reinstall Termux app from F-Droid.

If your Android version is 6 or lower, read https://github.com/termux/termux-app/wiki/Termux-on-android-5-or-6