You probably already know that we can not spot reduce. Spot reducing would be to eliminate fat in chosen areas like the stomach or where ever else you would want it to disappear. If it was possible I’d be a rich man but it’s not.
However, we can spot “tone”….kind of. We can at least train the underlying muscle to feel tight.
Our issue at hand is the fat that hangs underneath the upper arm. This is the triceps region. If we train the triceps adequately we can possible tighten the area. As a disclaimer, training a certain muscle does not burn the fat which covers it.
The exercise I recommend to train the triceps is Rope Extensions.
Attach the rope to the upper cable. With the thumbs pointing up and the hands facing each other grab the bottom of the rope just above the balls. With the elbows “bolted” in to the sides of the body pull the rope and straighten the arm. Release slowly and continue.