Male infertility (possibly)

My SO and I have been TTC since February, he thinks he has low T or is "shooting blanks". I've got one child from a previous marriage and he has none, he thinks it's him because I've gotten pregnant before, I think its me from issues with a mirena. I know we both need to get our fertility tested but what can we do at home, more so him than me. I'm already tracking my periods/ovulation, I'm going to start eating healthier and taking vitamins. What can he do to possibly boost his testosterone at home?