Hello there, this is a probably a very stupid question but I cannot find an answer anywhere on the internet and I'm getting pretty confused.

I have some miles I'd like to use for an award flight, but I can only login and search for flights operated by LH and its allies into the Miles and More website. I'd like to book a flight on United, but since I'm not a member of Mileage Plus I cannot login.

Am I supposed to call some telephone number and do it there?