Unplug your motors, select idle-up, center the left stick, look at the helicopter from the side. The blade should be at zero pitch. This is easy to see without a pitch gauge. Compare the blade to the flybar with the flybar held level. Adjust all three servo link rods equally by _full_ turns to raise or lower the collective pitch at this point so you have zero pitch at half-collective in idle-up. Full turns because the ball links are one-way.
Unless your upper pitch links are really screwed up this will give you the approximately correct amount of pitch in normal mode.
Or you can buy a pitch gauge.