Bad sperm mobility - any advice ???

Sorry if this is to much information but we are currently being tested for fertility and have just found out my partner only has 20% of his semen moving. Less then 40% is bad.

Does anyone know how to help in two ways:

1) To improve the mobility

2) How to tell him not to beat himself up about something that is unfortunate but natural

I love my boyfriend with all my soul and would love to give him children but we need help.

Thank you