I have had a lot of trouble using 71b with rhubarb wine. Try as I might, most of the time it fails to get started. I've had some luck at home with my small batches, but never could get it to work in the winery. I don't know if there is something in rhubarb that naturally suppresses this yeast. I fall back on ole reliable - EC1118. It never fails.
First - how does it taste and what is the pH? If it tastes ok and the pH is in a range that you can protect the wine, I would not mess with it.
A standard acid blend may be ok. But you certainly could add tartaric acid or citric acid. The latter would add some brightness to the flavor. If you have some of these acids already, try adding a bit to some samples and see which flavor you prefer.