Place the folder named wwshield in - 
mods\update\x64\dlcpacks

Now open OpenIV and 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:\wwshield\</Item>

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

Now you can equip the shield using Captain America Script or spawn by a trainer - (WEAPON_WWSHIELD)

Changes 2.0

Updated texture