look in the housing where it says av to know what input it is. Look on the board for the corresponding pins with the multimeter and solder it in the photo. I put this so that you can get an idea, this cable would also work.
Check the datasheet of the Main chip of the litlle board.
If you found it you know where to connect the Composite signal and you don't need the big board anymore.
GreatScott made good video on the subject :