While the switch is secured, grab a prepped wire and bring it close to the first terminal on the slide switch. Position the soldered tip of the wire to the terminals and hold it there steadily. Press the soldering iron against the terminal and wire to solder them together. You’ll want to do this gently and quickly. Ideally, you want the middle terminal be the “enable” while the far left/right be "ground", negative.
Once you’ve soldered up the three wires to the terminals, you’ll want to protect the connections with some heat shrink tubing. Cut a piece of heat shrink tubing that sizes for 30AWG wire to about 5-6mm in length. Slip these onto the three wires and position them over the exposed connections. Apply some heat to the tubing to shrink! Ideally want to use hot air.