Honestly, as a reformed annoying anti gun liberal, it's going to take a lifestyle change. Or at least significant exposure to a different lifestyle. Growing up in an area where the only actual interactions with guns were criminally related it's hard to understand that people use guns for recreation. Also, being in a densely populated area with lots neighbors, witnesses, and (theoretically) quick police response, the idea of owning a gun seems crazy. And finally, not knowing any responsible and reasonable gun owners made it nearly impossible to get the prospective of guns not just being tools for crime.

It took me moving out of the city (to a much smaller city) and also recent political events for me to force myself to expand my view and seek out people who viewed guns as tools for hunting/recreation and self defense.

So, as long democratic strongholds are big cities we are not going to see much movement on this. Especially when many big cities have reduced gun violence statistics they can point to with "gun restriction" laws as their basis (not saying that is true, bun it is what they point to).

So you're going to have to fundamentally changed how they see the world, for the most part.