The red dot, yes reflex site I guess, I am old school and to me it is a red dot, or green dot?
if you look at a burras mount picture, you will see a flat plate and a dovetail piece.
Push out the old sight, slide in the new dovetail piece,it is not tight, set the flat plate on the dovetail, with the two holes lined up with 2 holes on the dovetail, and install 2 screw that come with it and tighten the flat plate down on the dove tail, center it on gun, when you tighten the screws, it pulls the dovetail up and tight.
than you set your sight on 4 small posts on the base , install 2 more screws and that holds the site on the base.
Clear as Mud?
On this system, you don't use the weaver/ pict. base that comes with the sights.
If you had a rail on the top of the gun , than you would , and would not need the dovetail mount.
I have a mount for a sig, that I have not used, I could take a pic. of it , a bit different, same idea, could take a while to find, I think it is packed in the gunshow stuff.
But if you go to burras fast fire, they should have a picture.
I took me longer to type this , than it did to install the base and sight on the gun.
If you have trouble, it will be getting the original sight off, most come off easy, sometimes, not so easy., check for a set screw in the top of sight first.
P.S. there is a itybitty set screw on the top front of the plate to turn down to hold front of plate even on top of slide( elevation) sort of, I just set that so it touched the slide with out any pressure, as this was a new set up and it is fine , so I haven't messed with that, you have to take the sight off to adjust, if you elevation was way out you could raise the front of the base with it, but mine was close when I powered up in the shop.