1.) The first thing you wanna do is open up the folder after install called "Dante's Guns" From there you'll see 3 packages, the overall product with two empty gameobjects. They should look something like this:

2.) Once you do, go over in your avatar's hierarchy, from there open up your avatar's armature in the list and find your hips bone, along with both hands.

3.) Once you do, simply drag the prefab "Dante's Guns" onto your hips bone. Under "Dante's Guns" in your hierarchy you can select both holsters and using the move and rotate tools to adjust them to your base.
Do the same for the "Handhold" empty gameobjects for your hands. Put "Ebony L Handhold" in your left hand followed by putting "Ivory R Handhold" in your right hand

4.) Once putting everything in place, click on one of the two guns in "Dante's Guns" and find the "VRC Parent Constraint" on the inspector tab of your screen. It will look like this:

Under "Element 1" find the corresponding empty gameobject for the corresponding gun in your hierarchy that you just placed a moment ago. (e.g. "Ebony L hand hold" would go onto Ebony's parent constraint in "Element 1"). Do the same process with the other gun.

5.) After doing that, it's time to adjust the "Hand Holds" in your hand bones to make sure that both Ebony and Ivory are properly in your hands as you see fit. You will want to change the values of both Ebony and Ivory's weights as shown here:

Change Element 0's Weight to zero and Element 1's weight to one, This will snap the guns to the hands for us to adjust both of them. Use the move tool and the "Hand Hold" to move the guns in your hands till you are satisfied.

6.) After adjusting both guns revert the values in the VRC Parent constraint to what they originally were, they both should be back in your holsters. Once that is done you should be all set to upload! Be sure to test your avatar in the gesture manager before uploading to ensure that everything works.

here ya go, enjoy! (=^.^=)