Back up your data
Sign out of iCloud
Sign out of iMessage
Sign out of FaceTime
Unpair Bluetooth devices if needed
Shut down the MacBook Pro
Turn it on and immediately hold Command + R
Release the keys when the Apple logo or Recovery screen appears
Select Disk Utility
Choose Macintosh HD or your startup disk
Click Erase
Confirm the erase
Quit Disk Utility
Select Reinstall macOS
Follow the on-screen instructions
Complete setup or shut down if selling or giving away the MacBook Pro