Unauthorised user 4g router

[Hammerkop]

I have an unauthorised phone logging in to my 4G router. I can see it in settings. I cant see a way to block it. Could anyone advise please?

[XRaySpeX]

Change your WiFi pwd to be more difficult.

[Hammerkop]

Thank you for the response. Its a 4g router

There is a "secure key" on the back of the router which you use to access it.

Is this the number I should change? (and how do I go about it please?)

Thanks once again

[XRaySpeX]

Login to your MBB router at http://192.168.1.1 with username/pwd as "admin"/"admin" or with the password found under the battery cover. Then on the WiFi Settings tab you should be able to see your WiFi password in clear & change it.