Transmission will not shift why?

This could be a number of things but the most common thing is a fluid issue. Let's start with checking the fluid level and condition. Here are some guides that will help with this:

https://www.2carpros.com/articles/automatic-transmission-problems

https://www.2carpros.com/articles/how-to-service-an-automatic-transmission

Next we need to check for codes to find out if we have any there.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Then we need to more then likely drop the pan and find out if there is metal or clutch debris in the fluid. I attached the info from the manual on how to do this below.

Please run through this info and let us know if you have other questions. Thanks