This can be a bit of a fiddly job and requires you to disassemble the inner door trim to get at the workings within. The problem itself is usually a case of either the glass having delaminated form the metal track it rides it, or the winding mechanism itself has broken or rusted through or structurally failed in some other way.

Once you’ve removed the inner door panel and any protective sheeting under it, you should be able to see what’s failed or fallen off. You’ll need a good torch and perhaps even a mirror to see what’s going on in there as access can be tight.

If it’s a simple case of the glass having jumped out of its metal track, you may be able to refasten it with the correct adhesive. Often, though, it’s simpler and easier to find a replacement glass and track unit at a parts recycler (which we used to call a wrecking yard). If something else has failed, you may need to replace a whole lot more in terms of components, but until you can see what’s what, you won’t know for sure.

The other advice is to not try to move the window via the power window switch. Depending on where the glass is sitting, you may find the winding mechanism will bear on the glass where it shouldn’t and smash the pane or bend something important.

Fixing this would involve disassembling the door from the inside (removing the door card) to reveal the workings inside. From there, you can assess whether the glass has jumped out of the rail that supports it at the bottom, or if there's some other problem with the mechanism.

If it’s the former, you’ll need to find out what adhesive is required to fix it back into place. A windscreen replacement specialist might be able to provide this information. A Nissan dealer may also have the correct product on the shelf.

Replacing the glass might be a bit fiddly as there's a lot of gear inside a modern car door, including the side-intrusion bars, the window winding mechanism and the metal parts of the actual door. Some patience may be required.

If the problem occurred immediately after you replaced the carpet and seats, I’d say there’s a very good chance you’ve unclipped a wiring plug or connector to remove the interior, and failed to reconnect it afterwards. A lot of modern cars have airbags in the actual seat (the side airbag usually) and the wiring often runs under the seat.

The best move would be to remove the seats again and check for loose wiring or wiring or connectors that have been damaged of misplaced in the process of the interior’s removal. But before you touch anything under there, disconnect the car’s battery. That ensures you won’t have an accidental airbag deployment that could injure you while you’re working in that space.