Installing a cable grip in a floor usually takes two people. One feeds it in while the person inside screws on the locking ring.
This instructable shows how one person can do it easily.

Step 1:

Bend a hook on the end of a wire/rod then bend the wire into a horseshoe shape.
Place the locking ring over the hole to be used.

Step 2:

Feed the newly bent rod into the locking ring.

Step 3:

Bring the hooked end back through another hole and place a CGB onto it.

Step 4:

Feed the CGB through the larger hole by retracting the bent rod.

Step 5:

The hook prevents the CGB from falling off.

Step 6:

Guide the threads of the CGB into the hole.

Step 7:

While holding the CGB in the hole with the bent rod, screw on the locking ring.

Step 8:

Afterwards, fiddle with the hook and pull it back through the CGB. Tighten the lock ring and you're done!

Step 9:

If you have only one hole or to finish the larger ones, simply thread a string or rope down the hole with a hooked rod/wire attached. Go downstairs and place the CGB onto the hook. Go back upstairs and pull the CGB into place. Screw on the lock ring and tighten.