1) Find out about how he developed those attitudes. My first random guess would be media (Youtube, PvP online games, etc.), but you can't really rule anything out. Your goal isn't to pinpoint blame, but to get a better understanding of what your son's loosely moraled (to put it politely) influences are, and then to offer the counter-point to those, much like you would help a younger child process a particularly an uncomfortable scene in a movie.

2) Reinforce empathy in the most frequent-but-natural way you can. I imagine it will be difficult due to his age, so try to approach it as a team-oriented parent and not so much as an authority-oriented parent, if you can. I like to think of empathy skills as a muscle you have to flex in order to make it stronger, so don't hold back if you can hold some reasonable perks around the house until you can see him demonstrate empathy, especially when it comes to handling unpleasant communication from same-aged girls.

3) Incorporate his mom in the plan. This may have been obvious, but you really have to make sure you and her are on the same team and with the same playbook. Friendly fire is painful.

4) Notify his homeroom teacher, or the best person at school who fits this role (this would be more meaningful after lockdown). You would want the homeroom to understand how much of a priority empathy is to your son's education (and that of his peers). You can also encourage her to be more observant about his interactions with his classmates that may be connected (be careful how you interpret that information, though). Be easy on the teacher, though, because he/she will probably have a lot of other competing demand from other parents and the school. Also, communicating with the teacher in this way is NOT SPYING on your son, no matter what he says. As a parent, you have a right to communicate regularly about your son's non-academic development. Doing so will also help your son understand how important moral/social development is to you, and will start to be more mindful of your demands.

Hope this helps! But also, my advice does not replace that of a licensed therapist (professionals in the best position to help you).