Devious the kid going by this "there a 3 bubbles in my screen i saw then it turned black" alone, it sounds like a bad display. Of course, we could verify if we would have images showing what's going on. Since we do not, replace the disapply and re-evaluate. Something like this guide [guide|154307|Samsung Galaxy A12 Disassembly - iFixit Repair Guide|new_window=true] can help you with your repair. Of course, you can also follow something [https://www.youtube.com/watch?v=oBidM2ddc00|like this] video.