I can't really be of a lot of help because I'm just no expert on this.
But I've managed to take wheels that were quite crooked and make them reasonably straight.
One thing I can say is that you should tighten and loosen only a little bit at a time. Go slow.
If there's a bend toward, say, the left then you tighten those spokes that are anchored on the right. But only a little bit. And you loosen those spokes that are anchored on the left. But only a little bit.
Unless you're a 'natural' at it, you're not likely to get it perfectly straight the first time. Or the first several times. It comes with practice.
In the meantime you should probably just buy another wheel. Put that on your bike and practice straightening the wheel you have now. Then that one can be your spare.