How do I fix a crooked inside corner drywall line?
No need to mess with the tape job. It's just a matter of filling the depressions on each wall that create that wiggle. The easiest way is to completely repair one wall, then the other. It can get frustrating to try and do both at once, but it's possible. Your 12&quot; knife isn't quite ideal, but it'll do. A 16&quot; or wider knife or trowel would be great.
If you slide your knife against the adjacent wall into the corner you'll see that its edge creates a bridge over the recess. That's the level to which you want to fill. Lay some all-purpose or topping joint compound into the area. Press it in well, then work it out from the corner. Pull your knife out along the wall and scrape the mud flat. Use firm pressure but keep your knife no closer to the wall than about 60 degrees. You don't want it to flex into the trough you're trying to fill.
Always apply too little mud as opposed to too much. It's way easier to apply more later than to sand a mound down and deal with the mess. A fan makes drying times quick. Keep checking the level using your knife as a straightedge across the depression. At the end, give the whole area a thin skim to flatten any lingering divots.
When it comes time to sand, use a screen on a large pad. Don't use small sanding blocks.  They tend to dig into some areas more than others, degrading your flat surface. Use long, light strokes across the depression just until all imperfections are gone.