The zip-tie-on-the-fork method
Okay. We know what a wobble looks like now, and we know which side it's on. Time to actually fix it.
Here's the thing. Every bike shop's got a truing stand, this dedicated tool that holds your wheel and gives you a clean reference point to work against. Nice piece of equipment. You don't need one to start.
I trued my first wheel ever with zip-ties on my fork. No stand, no fancy gauge, just me, some patience, and a spoke wrench. Took me about an hour and it wasn't perfect when I was done, but it stopped the brake rub, which was the whole point. Honestly I still true wheels this way half the time. It's low key just as good for a wobble that's bugging you, not a wheel that's trying to kill you at speed.
What you're actually doing
A wobble means some spokes are tighter than others, pulling the rim off-center. Truing is just tightening and loosening spokes in small amounts until the rim spins straight again. The zip-tie is your ruler. It doesn't move, so it shows you exactly where the rim drifts.
Setting it up
Get your wheel off the bike, or leave it on and just get the tire clear of the ground somehow, a bike stand, flipping the bike upside down, whatever you've got.
Take two zip-ties. Loop one around the fork blade (or the seat stay if you're doing the back wheel) right next to the rim, on the side you want to check. Snug it down until it's stiff and doesn't flop, but leave the tail long. That tail is your pointer. Trim it so the tip sits maybe a couple millimeters off the rim surface, close enough that you'll clearly see it get closer or farther as the wheel spins.
Do the same thing on the other side if you want to check both directions, side-to-side wobble and up-and-down hop. Most of what you're chasing is side-to-side, so start there.
Spin the wheel slowly by hand. Watch the gap between the zip-tie tip and the rim. Where the gap gets bigger, the rim is pulling away from that side. Where it gets smaller, the rim's pulling toward it. Mark those spots with a piece of tape or a pencil dot so you don't lose track while you're spinning it over and over.
The actual truing
Spoke wrench, size that fits your nipples exactly, don't guess. If the rim pulls away from the right side at a certain spot, you tighten the spokes on the right side in that area and loosen the ones on the left, just a quarter turn at a time. Small moves. This is not a job for muscle, it's a job for patience.
Spin it again. Check the gap. Adjust again. You're basically negotiating with the wheel a quarter turn at a time until the zip-tie stays roughly the same distance from the rim all the way around.
That'll get you most of the way there. It won't be shop-perfect, but it'll stop rubbing your brake pad and it'll ride straight enough that you won't notice it under you on the Murdock trail or anywhere else.
Where people mess this up
Two things.
First, going too big on the turns. A quarter turn on a spoke nipple moves the rim more than you'd think. People crank a half or full turn because a quarter feels like nothing, and then the wheel's worse than when they started. Small moves, recheck, small moves again.
Second, and this is the one I actually learned the hard way, not from wheels but from chains: more is not better. I over-lubed a chain once, just soaked the thing, figured extra grease couldn't hurt. Did a full loop of the Murdock trail and by the time I got back the chain had turned into this black paste from all the trail dust sticking to it. Wrecked a good afternoon degreasing it back out. Same principle applies here. Don't overcorrect because you're impatient to see it done. Quarter turns. Recheck. Let the process be slow.
A real caution
Spokes can snap if you crank them too tight, especially old ones or cheap ones. If a spoke feels like it's fighting you way more than the others as you tighten it, stop. That one might already be near its limit, and forcing it can send it flying, which is unpleasant that close to your face. Back off and work around it instead.
Before next time
Grab a couple zip-ties and actually try this on whatever wheel's giving you trouble. Even if you don't nail it, you'll start seeing what a true wheel looks like versus a wobbly one, and that's most of the skill right there.