I've prepared sweet potato puree mix with bm last night and store in fridge. Can i feed tonight? Im not sure if i am suppose to blend with bm first & store?

Yes, frozen purée can last up to a month by conservative standards. Just ensure that ur purée was stored in a container that u can use a lid / clean wrap to cover - some people prefer to put this set up in a ziplock bag too to extra ensure cleanliness. Just that u warm it up evenly and mix up any separated portions

Yes you can still feed your LO tonight as long as it was immediately stored in the fridge and not previously exposed. I personally prefer to mix my EBM to puree just before feeding because some puree may get more watery in the fridge (or freezer).