How do we mark the numbers on the cards? I'm playing in IF.
If you have any photo editor, that should do the trick. If you are probably not aware of how to use that, an alternative is to use a laptop. Simply download the image, open it your downloads, right click on the image and open it either in paint/photos. ( If it's photos, you'll see an edit option, in that a pen like option, using which you can mark the Bingo cards). -- this is for Windows. Afaik, this is the same in Mac. -- except you'll not have paint, you can straight away open it in photos.
If it's paint, you can simply cross out the numbers you have recieved. I hope this helps.