For those holding Egypt Air bookings, how do you get your seat assignment?

I believe UA Award is booking into Fully Flexible fare buckets based on the free checked bags are 2 pcs. On Egypt Air website Full Flex fares have free seat assignment, but the lower fare buckets can pay for seat assignments.

Yet the UA tickets while showing on Egypt Air Manage Booking, the Services function is disabled - it is where you choose the seats as one of the "Services" options on a pay ticket.
On UA website the award AMM-CAI does not offer seat assignment function, but the LXR-CAI segment does, even though on Egypt Air website the same booking once again, the Services function is disabled.

Trying to call Egypt Air NYC reservation line, it is just an endless hold.

I am a bit worry of not having seat assignment on a partner award booking.

Anybody has successfully get their Egypt Air seat assignments before flying, your experiences are very much appreciated.