How do I evolve my eevee.. if there’s no specific “challenge”?

So I want to evolve my eevee into a sylveon, but when I try to, it says I must complete a challenge. My friend was able to evolve his into a sylveon and another into an umbreon simply by walking a distance.. but I can’t seem to get it to evolve. Is there anything I can do? Like- normally there’s a drop down menu- but there’s not. I’ve had this eevee as my buddy for a couple of months now and nothing works.