Submission from mount. Sometimes called the figure-four armlock.
To begin, isolate one arm and lay it out flat on the mat. Tired/new people may leave an arm out you can grab, but if they are defending chokes you can place a hand on the elbow and wrist of the same arm using monkey grips, get your body weight behind it and push it out and too the ground. When isolating the opponents left arm, monkey grip over their left wrist with your right hand and lay the right forearm along the ground with the elbow positioned against the neck. Slip the left hand under the opponents trapped arm and monkey grip your right wrist. Pushing down with the right and left wrist, and lifting up with the left forearm, drag the opponents wrist along the mat and down until they tap. Keep the opponents elbow at a 45° angle otherwise they won’t tap.