it is not too bad but time consuming if you are trying to get rid of the last 0.1 mm .
I locate the first and last spokes for the section of rim that is out, then loosen,tighten all the spokes in between as well by about 1/4 turn or less.
without a wheel truing stand you need to decide in which driection way to take the rim - usually that does not matter since the wheel will have been built up to be central.
That's my understanding. We'll see. Can't be any worse than it is now (famous last words).