Squeaking after changing belt and tensioner?

I would remove the belt and see if the squeaking is still there, it might have nothing to do with the belt, it could be internal to the engine. If the noise does go away spin the alternator and A/C compressor pulleys to see if you hear the noise, if you take a short video with your phone and upload it with your response that way, I can tell what's going on. Also make sure the belt is the right size because if it is too big the tensioner cannot hold the correct tension on the belt. Check out the diagrams (below). Let us know what happens and please upload pictures or videos of the problem.

When we changed the tensioner we turned it on without the belt and it did not squeak. Once we turned it on with the belt on it took a few seconds to make the squeak and it stayed. The belt is loose. I purchased the Continental Belt 4070407F.

Thanks for the video, you can see the belt is loose, it must be the wrong size, or the tensioner is installed incorrectly. Here is the correct parts number for the blet and instructions on how to replace the tensioner in the diagrams below.

Serpentine Belt - 117206TA0A - $53.05

Check out the diagrams (below). Please let us know what happens.

I purchased that belt from the Nissan dealership. We installed it but it is still squeaking. The belt does look loose but not as much as with the continental belt.
We tried again turning it on with no belt and there is no sound with no belt.

Yep, it is a belt issue. Can I ask if you got the tensioner from Nissan as well? The belt tension is not enough that is why it makes the noise.

The tensioner is from Nissan.

There is a timer in the rear of the tensioner can you see if it is installed correctly?