My split pea soup is bland
Look for recipes and add in the things your attempt is missing.

The common denominator will probably be meat (ham bones are common), more salt, and pepper to taste. If you want to take a shortcut, you could use bouillon cubes or paste to provide both meaty flavor and salt, though pork is a lot harder to find than chicken or beef.

Salt and pepper you can just stir in. Same goes for bouillion cubes/paste, though you'll want to mix them into a small amount of soup first to get them to dissolve well and then stir that into the rest of the soup. If you want to add real meat, you'll want to cook it a while longer to get the flavor into the soup. Additional herbs and spices you'd also want some additional cooking time - the simplest rule of thumb would be to just look at the recipe and see how long it cooked the soup after adding those ingredients and do the same with yours.