The chain is as tight as a ***; can't move it an inch/mmOr you could try just putting the chain back on the pulley wheels first. You should be able to raise the end of the tensioner with your finger to get the chain back on. If you can't then there's a problem with the tensioner.
Ordinarily, I'd say swing the back end down as that releases the tension on the chain (hence the need for the chain tensioner in the first place). Have you already done that? It's hard to see from your pics, but I'm assuming you have as your luggage rack is on the floor.The chain is as tight as a ***; can't move it an inch/mm
I just undid the chain. I had a look at the chain tensioner and when I align it with the other fixed little gear, they are not. I also think I can visible see that part of that tensioner is damaged.Undo the gear cable then undo the hex bolt. That will enable you to take the chain tensioner etc off , and free up the chain. Then put it back together in right position.