It appears that it is suffering from drying out - and who knows what other abuses. First, get it out of that white ceramic pot which will probably not have any drainage. I assume it is in a black nursery pot on the inside(?) Remove and toss that fake moss on top of the soil so that you can observe the soil surface. Was the tree inside the store (in the area where they hold their tropicals)? Or was it outside? I can normally tell how watered my trees are just by lifting them. At this point you want to water the tree, and leave it alone until it almost dries out again, and then water once more. Do not keep the soil saturated like a swamp. Do not trim, or do anything to the tree, including pulling off any of the old leaves. If you have a bright window, leave it in the window and hope for some sign of life.