This may be OP's question
Premier Executive priority services
First in line: Priority check-in
Check-in for your United flights at the counters designated specifically for you. If no elite line exists, you are welcome to check in with our United FirstŪ customers at most major terminals in the U.S. and Canada. On international flights, you may check-in with our United BusinessŪ customers.
So if there is no elite check-in you can use the FC check-in
as
gomike said in boarding 1Ps always use the regular boarding line but will board before Seating Area 1