Two ways.
1 - use hall sensors to start motion, switch to encoder commutation as soon as you detect halls switching to next position. It's very accurate, unless you are using Chinese crappoor quality (in which case hall sensors wouldn't work at all). 2
2 - use current to move the rotor into a known position. then you can work without halls, but there are lots of nuances - friction, end of motion, current limits, etc.