Q.How do I help my sick blueberry bush?
I bought my blueberry bush recently and it had some broken spots on the leaves. Now all of the leaves are brown and curling.

There are many pests that can be causing the leaf damage on your Blueberries. A closer inspection will be needed to determine the pest.
You can treat with Neem Oil, which is organic and will treat most sucking pests.
Here are some links to help you.
https://www.lsuagcenter.com/topics/crops/fruits_and_vegetables/blueberries/pests
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm