From what I’ve been told, if you print that part (the switch lever) in pla , it’ll probably not last long.
But to answer your Q….. a picture paints a thousand words, an all that.
Here’s Stupid Airsofts video fitting it, a two second job
View: https://youtu.be/clAg5oPy3F4?is=AAnXwtNActOEIfUb