how to use BMO World Elite perks (bag, seat selection)

I booked a Porter flight prior to getting the BMO World Elite card. Now that I have it, my profile shows my VIPorter Venture status but my reservation doesn't allow me to select a seat or add a checked bag for free.

Is there any way around this? Is it like Aeroplan where you only use the benefit when checking in 24h prior to the flight?