1) Device > More Options > Adjust Input.
2) How do you change inputs for your TV using the original remote?
Select "I go directly to the input I want", then click "Next" at the bottom.
3) Review the list of inputs and, if necessary, make changes by editing the Input Names.
Note: These are input labels not commands. Click "Next" at the bottom.
4) What command do you use to get your device to go to this input xxx.
Select "I don't have the original remote, but I know the commands that are used".
Click on the little "v" symbol to see the list of commands (drop-down list), and select the correct one you found worked in device mode. Click Next and repeat step 4 for all inputs.

Note 1: The database entry (dataset) for you device will have a lot more commands that your OEM remote because it represents the entire "brand" rather than just your particular model. Just ignore your OEM remote. Use it only to teach missing command(s) if applicable.

Note 2: When I added your "Mitsubishi LT-46231 TV" device to my setup, it did not ask if I have the original remote. So I don't know why you keep mentioning that the website is asking you to press button on your original remote.