FlyDubai allows you to make a reservation with the airline and upgrade it to business class later. However, you must read the Flydubai business class upgrade policies before applying for it. Here are the policies mentioned:  

Flydubai can deny your upgrade request at any time.
The passengers must pay the difference in the fare between the two cabin classes.
Travellers can bid for seats in business class.  

How do I upgrade my seat on Flydubai?

The passengers will have to request an upgrade to the airline. Here is how you can request the airline to upgrade your seat in the business class:  

Visit the official site of Flydubai.
Locate the “Manage my Booking” option.
Enter the passenger’s last name and the PNR number to get your booking details.
Once you get the booking details, move to the menu and select the “Seat Upgrade” option.
Get a seat map on the next page, enter the preferred cabin class, and select your seat.
Move next to make the payment, and the airline will email you the status of your upgrade request.  

How do I contact Flydubai for a business class upgrade?

Travellers who have doubts about seat upgrades or are having difficulty understanding the online upgrade procedure can dial 600 544 445 and speak to the airline's agent for help. You can also upgrade your seat to business class by dialling this number.