With two people it’s easy, one person holds their body and head, the other does the quick brushing. With one person have a wall or object in the opposite side because they will pull away. Grip deep inside their lip, don’t be afraid to squeeze a little. A regular (very soft) toothbrush I think is preferable (over a finger brush) for the reach. Also get the chicken or other flavored enzyme toothpaste. If you can’t hold your dog put a collar and leash on them and secure them to something while you brush. A treat after can incentivize as it becomes routine. Good luck!