5g nr5103 Router re-sold by EE in UK

I was supplied this router by EE in the UK and it works fine with EE. I want to change the network to Vodafone but the APN area within the router profile settings are set to EE  with their own software they have loaded onto the router. It will not allow me to change the APN settings. I have spoken to EE and they have informed me that you, Zyxel stated the router is unlocked and EE have also confirmed the router in unlocked. However, I am still not able to change the settings. If I install the Vodafone SIM it will not download the APN config file, neither will it connect to their network. I have tested the Voda SIM using my mobile and it connected OK and downloaded the config file. It is just the router that has the issue. Can you please advise on how I can either default the router to the standard Zyxel OS/ firmware or how to access the EE profile page to allow me to change the APN info.