Plug in type c cable connected to pc. Hold volume down and power button together. As phone turns off remove volume down button and hold volume up but keep holding the power button. As soon as you see samsung a71 logo leave power button but keep holding volume up. Then you can select factory reset option.
Dear Samsung Member,
Greetings from Samsung Customer Support!
We would request you to register your concern in Samsung Members Application. So, that our concern team gets back to you as soon as possible.
Please follow this path to register your concern in Samsung Members Application (Open Samsung Members Application > Get help > Send Feedback > Error report/Ask questions).
Note. please attach the error log file within 15 minutes of the error occurred.
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Samsung Customer Support