My fiancee is 23 and he has just found out that he has low progesterone and motile sperm. we're trying to conceive. what does he have to do conceive?

Problem not clear: Presumably you mean "low testosterone", since there is no reason to measure Progesterone in a male. How low is low? The range of normal is broad. If he is able to perform sexually and has normal sperm count, and good motility, then he should be fine.

See a REI specialist: You both should see a fertility specialist (rei) for help. He may benefit from weight loss, stopping smoking or aromatase inhibitor pills (if he has low testosterone with high estrogen). If you're 40 you should also get checked out for low egg supply (diminished ovarian reserve), ovulation or hormonal problems, damaged/ blocked fallopian tubes, endometriosis, and fibroids or polyps in your uterus.