I'm NOT an expert but in my experience (I had a blueberry bush on my balcony for a few years) blueberries much prefer to be not fussed with and to self-fertilize.
What's the moisture level like in the soil?
Blueberries also like lots of water but to dry a bit between waterings. Mine like a good soaking every couple of days during summer.
Is there any elasticity to the branches and are the leaves green? If so, it might have just become stressed and needs some sun and water and to be left alone.
If there's no elasticity and the leaves are dead then you might need to replace the bush.
Hope I helped.