So I think I did something to erase something important off my card, it’s empty on my computer (iMac) but reading full on my camera (canon eos 70d). Think I may need to re format. I’ll be doing this on my iMac just incase the process is slightly different. Thank you in advance.
Are you trying to erase the card? I think the reason it shows empty while connected to your Mac and full while in your camera is that unless you empty your Trash while connected to your Mac, the files aren’t actually erased; only the reference in Finder to them.