Heavy seated DB shoulder presses.
Then focus on lateral and rear delt work... that's what'll round up your shoulders...
Standing single hand lateral raises, go heavy and focus on the tension, perfect form is bs, the function of the lateral delt is raising the arm.
And rear delt work, bent over raises/rows, reverse peck deck. They can be hard to grow for many people, some people will emphasize light weights, I think it should be a combination of both going heavy on some cheat reps and high rep lower/moderate weight. Everyone responds differently however...
Any kind of rowing back work will work rear delts too.