Automatic Transmission Warning Light

[white lancer]

I replaced my expansion tank last night and after I completed the job I ran the car for about half an hour ticking over outside the garage to get the car up to temp to check for leaks when the radiator system was pressurised.

I left off the air filter housing and Mass Airflow Sensor whilst I was running the car so I could get a better view of any leakage.

I noticed afterwards that there was a yellow warning light on the dash. it is a little yellow circle with an exclamation mark in the middle. I looked in the manual and it states Automatic Transmission Warning Light.

Is this related to what I was doing? Will this dissappear on its own or will I need to reset it?