Samsung SM-A405FN/DS User Manual page 145

Settings
Registering fingerprints
On the Settings screen, tap Biometrics and security → Fingerprints.
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Read the on-screen instructions and tap Continue.
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Set a screen lock method.
► Galaxy A20e: Swipe your finger downwards over the fingerprint recognition sensor.
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► Galaxy A40: Place your finger on the fingerprint recognition sensor. After the device
detects your finger, lift it up and place it on the fingerprint recognition sensor again.
Repeat this action until the fingerprint is registered.
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When you are finished registering your fingerprints, tap Done.
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