Replacing this RTC battery is a straightforward process. You will need a standard Phillips screwdriver plus a small cup to hold the screws.
Find the plate on the mount where the hand control plug is located. There are eight Phillips screws on this plate. You will need to remove the four corner screws. Place them in the cup so as not to lose them.
Gently pull the upper edge of the plate down and out so as not to disconnect the internal wiring. On the top right edge of the visible printed circuit board you will see the CR2025 RTC battery. Use either a long fingernail or a small screwdriver to carefully pry the battery out. There is a small clip towards the left side of the battery holder that will release the battery once the opposite edge is raised.
Remove the battery and replace it with an identical CR2025 battery. Be sure to insert the battery with the correct polarity (positive facing outwards).