so my front wheel is perfectly true, but runs about 10mm off to the left on both sets of forks i have (ie it hasnt been dished properly and it isnt a wonky fork dropout).

So i need to dish it over a bit.

do i just simply loosen the spokes one way a bit and tighten the opposing side? if so how much should i start with 1/2 turn?

do i need to take the tyre off (running tubless so this will be a faff?) to preempt the mocking i did mention numpty in the title.

i can always take it to the lbs but id prefer to learn as i have the time…..

Tyre on is fine.

1/2 a turn is good to start with. Loosen the rhs first the tighten the lhs. See how far that's got you then do more if nec. You can tighten without loosening once you are close.

10mm is a LONG way out. where did it come from?