Originally Posted by
dh01
You cannot, you have to call United and ask them to search. Business class seats are very hard to come by with United miles, but they are sometimes available.
SQ rarely (never) releases premium cabin inventory to partner airlines, including UA, on their long-haul flights. You can use ANA's flight search tool to look for SQ inventory, but for DME-IAH, you're probably wasting your time. It's common to find availability on intra-Asia flights, but not transoceanic travel.