On the end of the push button there’s a screw and you’ll need a very small Phillips screw driver.
The screw doesn’t completely remove, you only need to loosen it.
The button will come apart.
There are four(4) small springs that will probably come off when you open the push button, don’t lose them!
There are four(4) batteries CR2016 that are required. Two(2) on top of each other.
Prior to putting the button back together you will need to put the springs on each corner of the opener (see picture).
The opener only goes back together one way, on the opposite side from the screw is a lip, you’ll need to insert the one end into the lip then close the two pieces, careful not to lose the screws.