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Go to iManager >Utility tools / swipe up on the screen > App encryption > set up a password > App encryption > turn on the app switch to encrypt it. Or you can go to Settings>Face and password/Fingerprint,face and password/Security>Privacy & app encryption>set up a password>turn on the app switch to encrypt it. Then you must enter the password you set to open the encrypted app, which could help you protect your privacy further.