WN1000RP can not change to new isp

I have changed my isp company but can not connect with my booster. I have poked the reset button, it still reads the id as previous isp company. I assumed it would reset back to netgear, connect then let me enter my new password. I tried entering the new password but it goes to authorising then just saves and doesnt connect. I can not use the 'my wifi' page as i am not using booster to get online so it says can not find it. I have looked through an online manual and find nothing helpfull . I have tried with my tablet and computer. How can I get this to work? I am a bit of a computer novice so it is probably something I am doing wrong, any help  appreciated (as simple as possible please). Thank you

Jenny