Lamar Odom is reaching out his hand to Bam Margera in the midst of all his substance abuse and legal problems, saying he's more than happy to help, free of charge, if the reality star allows it.

We caught up with the former NBA star in Manhattan Beach, CA and he offered some advice for the former "Jackass" star ... hours after Bam turned himself in to PA cops for allegedly assaulting his brother.

Lamar says, his first piece of advice is for Bam to lean into religion -- if it's something in his life -- to help him during his troubles. LO also personally invited BM to one of the 3 wellness centers he co-owns and operates, called Odom Wellness Treatment Centers, to address substance and drug abuse problems ... reminding us, he's been through it too.

As we reported, Bam surrendered Thursday to face charges in Pennsylvania for allegedly attacking his brother, Jess, last weekend. Cops say he threatened to put a bullet in Jess' head before going on the run. Bam denies that's how the story unfolded.

Regardless, he's been dealing with a ton of issues lately -- most of them seemingly tied to his addiction and mental health issues.

As we reported, the 2-time NBA champ acquired 3 rehab centers in Southern California and is now on a mission to help others in need. You'll recall, LO overdosed at a Nevada brothel in 2015 and suffered kidney failure, heart attacks, and several strokes ... but he's been able to turn his life around.

Lamar says he's welcoming Bam with open arms if, and only if, he wants the help. He left off with a simple message to BM ... "I love him and just stay strong."