Please note, before reset to factory settings you must log out of google account and mi account. Otherwise, after a reset you need to enter data for previously established accounts. If you don't know them, then after a reset works FRP lock.
For Xiaomi Redmi 5 plus reset to factory settings is via Mi-recovery. The algorithm is as follows:
Turn off the phone
Press and hold both "Volume +" and "Power"
After the Mi logo appears release the buttons
After some time there will be Mi - recovery
With volume buttons select "Wipe data" and confirm with the "Power" button
Then select "Wipe all data" and confirm with the "Power" button
With volume buttons, select "Confirm" and confirm with the "Power" button
After formatting, user data, select "Back to Main Menu" to return to the main menu
Select "Reboot" and confirm with the "Power" button
