It’s all in the checklist for unreliable airspeed.
Check pilot’s airspeed, check FO’s, check the standby, work out which one is faulty whilst referring to the documented power setting and climb angle that will give a consistent S&L attitude.
Turning back by hand flying without determining which one is at fault / which one to trust is fraught with danger. Elevator starts to get spongy / unusual feelings, because the computer generated feedback to the controls is up the creek because it thinks you’re at a speed that you aren’t and won’t let you pull hard at times.
Turn gets tighter, speed looks to be decaying, turns too tight and puts it into a dive, going from 300 knots to 600 knots and parts start to fall off.