Place the folder named capshield 
inside -Grand Theft Auto V\mods\update\x64\dlcpacks

Now open, OpenIV go to this location
Grand Theft Auto V\mods\update\update.rpf\common\data

Extract dlclist.xml and edit it.
add this line like any other add-on:

<Item>dlcpacks:\capshield\</Item>

now save it and replace the old dlclist.xml with the one you just edited.

ingame press CTRL + i to toggle the menu. From there you can equip the shield and enable powers!