Hi,
In order to use the AirPrint technology, a printer must be AirPrint-enabled.
About AirPrint - Apple Support
Which exact Brother printer model are you using?
You said that the printer is connected to a PC. AirPrint is not supported on a PC (but there may be special third-party desktop applications working together with an iOS/iPadOS app). Or do you mean a Mac computer? How is the printer connected (USB or network)? Please mention any special app involved.
Generally speaking, if an iPad cannot see an AirPrint printer, one could try the following procedure:
Power off the Wi-Fi router, the printer, the iPad, and all other devices/computers. Wait two to three minutes. Power on the router. Wait two to three minutes. Power on the printer. Wait a minute or two. Power on the iPad. Finally, power on all other devices/computers.