This is a switch case that you can use to enclosure commercial ESC (like Modelsports
XT-12 or
XT-20) or create your own switch to replace tiny ones (like the one present in the commonly used Hobbywing Quicrun
1060WP).
What you need is to buy a common slide switch like
THIS ONE and solder wires to the existing ESC.
The case has a pass through hole for the cable and has a recessed arrow with ON word in order to identify the correct position of the switch once enclosed.