Lots of options - especially since you're 1K.

UA *may* be able to print your LH BP, but I've had very mixed success.

By far the easier route is to checkin online with LH directly - an added advantage is that as *Gold you'll also be able to select a seat then. Your record at ua.com will have a link to your LH PNR, which is what you'll need for the LH system.

Or, you can do it at the Senator Lounge in FRA, even if you've checked in already, have them check it at the lounge and (in my experience) they may reprint it. If you have checked bags they'll also enter that into their system, which will save time at the gate.

I have NOT had good luck checking in for a LH flight at a non-originating airport (as in at ORD for a FRA-XXX flight) they told me it couldn't be done and to wait until I got to FRA. This is why Online is my preferred option.