What model DirecTV remote do you have? Look for number on top front corner.
If it's an RC6x (e.g. RC65R, etc) that's programmed to control your TV, you should be able to program the TV's INPUT button as follows ....
Activate TV INPUT button:
Mode switch to TV
Press and hold Mute and Select until the LED blinks twice
Enter: 9 6 0
If the LED flashes twice after entering 9 6 0, the Input button is enabled. If it flashes four times you've turned the Input button Off and need to repeat the above step to enable it again.