If you don't have a truing stand then I would do it in the frame. Once you've re-spaced it put the tyre back on but deflated and set the wheel in place. Tighten the nuts to a bit more than finger tight and you'll see how far you'll need to dish it. If it's more than a couple of mm then you may run out of thread on one side. Loosening the other side means reducing the overall tension on that side which you'd rather not do if you can help it.
Anyway, once you have the wheel in place loosen off all the nipples by a half turn and put a half drop of oil (chain lube will do) between each nipple and rim hole. Wipe off any excess. Then tighten by a quarter turn in the direction you want the rim to move on one side. Hopefully this will be the drive side of your wheel. If you need to move it further go round again by another quarter turn. You can go a third time and you'll still be fine.
Next check the overall tension of the spokes. Grab adjacent pairs with your hands and give them a squeeze. If they give easily then you can take the overall tension up a notch. Perhaps a half turn per spoke. If they start creaking a bit when you are about there.
Check for lateral truing by sellotaping a pencil to frame so it almost touches the rim. You know what to do here. You can work with one eighth turns if you want to get it to less than half a mm. If you get stressed either stop or have a beer. But only one mind. It'll calm you down and keep you focused. You have to true your mind as well as the wheel.
If you don't have a truing stand then I would do it in the frame. Once you've re-spaced it put the tyre back on but deflated and set the wheel in place. Tighten the nuts to a bit more than finger tight and you'll see how far you'll need to dish it. If it's more than a couple of mm then you may run out of thread on one side. Loosening the other side means reducing the overall tension on that side which you'd rather not do if you can help it.
Anyway, once you have the wheel in place loosen off all the nipples by a half turn and put a half drop of oil (chain lube will do) between each nipple and rim hole. Wipe off any excess. Then tighten by a quarter turn in the direction you want the rim to move on one side. Hopefully this will be the drive side of your wheel. If you need to move it further go round again by another quarter turn. You can go a third time and you'll still be fine.
Next check the overall tension of the spokes. Grab adjacent pairs with your hands and give them a squeeze. If they give easily then you can take the overall tension up a notch. Perhaps a half turn per spoke. If they start creaking a bit when you are about there.
Check for lateral truing by sellotaping a pencil to frame so it almost touches the rim. You know what to do here. You can work with one eighth turns if you want to get it to less than half a mm. If you get stressed either stop or have a beer. But only one mind. It'll calm you down and keep you focused. You have to true your mind as well as the wheel.