A "finger brush" refers to a toothbrush-like tool that fits over your finger, allowing you to brush your teeth with your finger instead of a regular toothbrush. Full definition
Eventually, you will want to introduce a small, angled brush or a rubber finger brush as well. (thedrakecenter.com)
I would definitely recommend not trying this until your dog is completely happy with the manual toothbrush, or finger brush method I describe above. (pethelpful.com)
Next, put the toothpaste on a small finger brush or toothbrush and slowly introduce to your pet's mouth. (aaha.org)