Did it not go through malolactic fermentation when it normally does?
You could mess with the acidity, which could be tricky to pull off. Also it may trade one wine fault for the other. However, since you are aging it on oak right now, you could perhaps make a "lower than normal" acidity white wine this coming season. Then, after both primary (and perhaps secondary?) fermentation is complete, you could blend the two together. Do a little trial before you blend it and see if you like it. If not, no harm done. You can always add acid to your new wine and get it where you want. It won't help your older, tart batch, but it won't be any worse off than before.