u/Background-Seesaw761

i have a 6 month pomipoo (maltese, pomeranian, and poodle). he's the sweetest baby to me, my family, my partner, and select few dogs. though, when i take him on a walk or when he's around my friends, he is aggressive. he hates strangers and unfamiliar dogs and will grow, bark, and has even bit at dogs. i do believe the man i bought him from was mean to the dogs he raised, so it could be trauma. i'm not for sure and i really need help fixing this because i just want him to make friends with other dogs to play with and be loved on by everyone. if anyone could help tell me how to train this out of him please let me know.