[Please help!] Question about Crescendos/hairpins

Hello, I'm very new to musescore, and I'm having trouble with hairpins. I know how to make them so that in a sequence of notes, it gradually gets softer/louder, but I don't know how to make it so it is just one note, that gradually gets lower/softer. So just answer this example question please: I have a whole note. It starts out forte, but by the end of all four beats of a whole note, it will have gradually gone down to piano. How do I do this?