This is a combination of a static hold and regular press.
-Press both dumbbells up. One stays up as the other lowers and performs one rep (technically half of one full rep if you include both arms). Always keep a slight bend in the extended arm while paused. This will increase tension on the chest.
-Focus on keeping both shoulders back and your chest pushed out. Keep good form even as your chest begins to tire.
-I recommend a 1-1, 2-2 style count like most single arm exercises.