Thanks everyone for your suggestions. I called Delta for my AS and KE confirmation numbers because they are not listed in my confirmation email. The Delta CSR told me that AS will recognize my Elite Plus status but KE won't.

I logged into AS site. It allowed me to select preferred seats due to my Elite Plus status.
I had a hard time navigating KE site so I called. The CSR said she could select seats for me but I wouldn't get preferred seating. I asked for seats as front as possible but was given 41 to 44th rows even though I saw many other seats available from Flydetal app.