When is your flight?
As the screen says, OLCI opens at -24 hours. (If you see anything saying that it's -24 hours for Exec Club members and -12 hours for everyone else, ignore it - that's changed.)
If you've not yet reached the -24 hour point, look for the link that says "Request a seat". If there are seats available that you'd prefer, move yourself via that screen. If not, wait until OLCI opens. If you're really keen, you can go back in to your booking from time to time to see whether any good seats have been given back to the system, but it's pretty much pot luck whether anything happens. When OLCI opens, you'll have a reasonable chance at getting at the seats that are held back and not allocated until check-in.