This is a basic mounting for a SG90 servo designed to secure it to control model railway turnouts from below the board.

you will also need a short length of piano wire with a "Z" bend in one end to hook through the servo horn and to drill a 1mm hole - it is present in the design but on a low quality setting my not print, you can see where it goes though

the servo clips in and out from the rear, the mounting can be screwed or glued to the baseboard as required