Installing VRidge for GearVR is very simple and it only requires few click. First of all install SideloadVR for GearVR app from Google Play HERE.
Then open SideloadVR app and your OSIG should be automatically set.
However if OSIG wasn't validated then go to SideloadVR navigation menu -> Manual OSIG Setup and follow the instructions on your screen.
Once your OSIG is configured, search for "Vridge" (without quotation marks) in SideloadVR app and install VRidge 2.0. VRidge classic is older version and is no longer being updated - it's highly recommended to use 2.0 version.
NOTE: Installation of VRidge for GearVR might be blocked by Android. To fix that simply go to Phone Settings -> Security and check "Allow installation of apps from unknown sources."
After the installation is complete, look for VRidge for GearVR in Apps on your phone, open it and put your phone into GearVR, start RiftCat client and enjoy PC VR games on your phone!