Heat only coming out of drivers side

I am a single lady who bought a one owner car from an elderly lady. To the best of my knowledge the automatic climate control for the passenger side had never been used until my Grandson used it to adjust the air on his side. Since then when I go to use the heat it only comes out on the drivers side and cold air comes out on the passenger side. Once in awhile it will open properly and blow out both sides. Heat comes out the back just fine but on defrost it is only cold air. Do not know if that is normal.
I was just going to go ahead and order the actuator blend door part but thought I would get a second opinion.
If this is the problem can I access this from down on the floorboard and under the dash of the passenger side?