Nighthawk m1 and o2

hi I wonder if anyone can help, I have a new to me m1 router and an o2 data sim.  I'm not sure if I have the apn right but they started the sim, I got 300 b use and I just can't find a way to top up the card.  I'm not sure if the router is set up properly and o2 are not being particularly helpful.  I'm new to this type of router, I have googled, I have live chatted, I have phoned, I have read, I am still lost and not working.  Any clues?

thank you, jon.