How can I refactor yield result usin async?

Question

I am working with async. I have an async function that resolves to a prompt

let myalt = (me) =>{

  alert('Hello ' + me)
}

async function greeting  ()  {
  return
  prompt('Helame');}
greeting().then(
function (val){myalt(val)});

and .then to an alert but I get undefined.