Those concentrates contain acid already , so don't add acid blend to them. You can try to add some tannin to it to even it out or,
When it's time to rack them, top off with water or hit it up with a commercial wine that similar to cut that sourness.
I pick up a Carlo Rossi like wine that's a gallon and decant them in 750's to use as a cutter/top off.
This way you get a new gallon jug to make another wine in, plus you get a few bottles of wine to add to the cellar.