It sounds like you are having either a pressure issue or manual valve issue. Basically when you put the vehicle in gear, the shift linkage moves what is called a manual valve and this is what directs the pressure to the correct portion of the transmission to engage that gear.
We need to start with checking for codes even though the light is not on.
https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing
If you have no codes then we need to find out if the shift linkage is still connected. If it is then we need to check pressure and find out if the pressure is correct. I attached the process and it is pretty easy to check, we just need to rent a gauge to do this testing.
Let us know if you have questions but this will determine if we need to go into the transmission or not. Thanks
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Thursday, January 28th, 2021 AT 3:29 PM