Shifts into gear when cold, but not after warmed up?

More than likely we have an internal transmission issue that is happening when the fluid is hot.

This means we need to start with checking the fluid level when it is hot and see if it is the correct level and the condition.

https://www.2carpros.com/articles/how-to-check-and-add-transmission-fluid

Then we need to drop the pan and see how much metal is in the fluid and pan.

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

The next thing to do is put the pan back on if there is no metal and check the pressure.

So, refill the unit and use the info below that will help with checking the pressure in the unit.

Once we know what the pressure is when it is hot, we will know what next steps to take.

However, if the fluid is new, there is no metal, and the system is full, and you have low or no pressure when it is hot then you have an internal leak, and the unit needs to be rebuilt.

Let me know what questions you have. Thanks