There are three popular ones that can be used by your therapist or even by yourself.
1/ Ballooning Technique
This technique makes your erections last longer and regular massaging allows to remedy your premature ejaculation as well as assist in prolonging it. Making your stamina stronger. Massage your penis using oil eg baby oil, jojoba oil, any base carrier oil you may add some essential oils for relaxation if you like to like lavender, rose, ylang ylang. Massage your penis with firm stroke till you get a passable erection. then just concentrate on the base and the scrotum part of the penis and intermittently press it firmly like holding a balloon. At the same time with the other hand press on the tip of the penis. Doing this can accelerate testosterone production and can help to prolong your erection as well as overcoming impotence. Practice several days in a row and be amazed with your improvement.
2/ Milking Technique.
So called because it resembles milking a cow. Using three fingers - thumb, forefinger and third finger to encircle your penis' base start with your left hand firmly move from thee base to the head of your genital head then repeat the process with the other hand. Regular practice will enhance the growth in the corpora cavernosa that prolongs erections.
Using oil massage the penis till you get a passable erection then using your right hand slapping it gently on to the palm of the left hand like giving it an invigorating workout.
Corpus cavenosum are found along the length of the penis. They are found along the penis shaft, from the public bones to the head of thee penis. This spongy tissue fills with blood and the blood comes from the arteries down the length of the penis. the blood fills the corpora cavernosa and causes the penis to gorge. When swollen it holds 90% of the blood involved in an erection and this helps to increase both the length and girth of the penis. Blood can leave only through a system of veins around the outside wall of the corpus cavernosum. The expanding tissue constricts these veins. This preventing blood from leaving. The penis becomes rigid as a result. -wikipedia