That just creates a string that repeats string n times. Nothing more to it.

A more Swift name would be:

func repeat(string: String, times count: Int) -> String

or you could use a method on String

extension String {
    func repeated(times count: Int) -> String { // implement }
}

These functions are against Swift naming conventions. func repeatStr(_ string: String, _ n: Int) -> String. Global functions, the term Str, blank external labels and n as an internal label are all against Swift naming guidelines.