What can a woman do to help a man stop ejaculating early?

Perineal pressure: Apply pressure to the perineum with a fingertip prior to ejaculation with a gentle massage motion.

See below: 20 to 30 percent of men experience premature ejaculation. Specific behavioral and physical techniques include: “stop-start” technique; “pause and squeeze” technique; “sensate focus”; and pelvic floor muscle exercises. Pharmacological treatment includes oral medications and topical “numbing” creams/sprays. I would encourage you and your partner to educate yourselves further on the details of these.