first off, mount a pen on your forks pointing at your rim, and spin the wheel a few times. This will leave a pen mark on the parts of the wheel that are buckled so you can stop spinning it all day and trying to catch the wheel at the buckle.
Next, take your spoke wrench (a spanner really won't do much - trust me). All you need to do is loosen the side where the buckle is, and tighten the oposite side in effect "pulling" the wheel back into place. this will in effect put tension back on the other side so your spokes aren't loose. EASY!!
You only need turn the spoke nipples at max 1 turn at a time and alternate between about 4 - 6 spokes (2-3 on each side). After some patience, and a few cups of tea, you'll have a nice straight wheel ready to go out and bend again. Lovely
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