So long as you're not in a backbow, there's nothing really to "fix" other than you'd like to know if you needed to, you could get a little more bow out of it. To fix it you need to get some bow into the neck. I use heat and pressure. You're not just trying to make the wood shift as much as you're loosening the glue joint between the neck and fretboard, so when it hardens again it's hardening in a bowed position. But you never really know what you're going to get when you do that. It can be a temporary or permanent solution. A totally permanent solution is to wait until you need a refret, and then either open the slots a little or use smaller tanged frets. Then the neck would be "weakened" enough to pull into a slight bow under string tension. Some guys would just plane the bow into the board, either with a neck jig that simulates tension, or by levelling the board with the truss rod torqued. That's alright, but not my choice. If you wanted to do a fret level with tension or a tightened rod, I'd say that could be your best intermediate and least destructive fix. If it still plays like you want it to, but with too much low E noise, that's the best fix.