Default BT Yahoo Not Working on Gmail

Hi;

Up until recently I was happily using the Google Mail App on my HTC DHD to receive Google Mail and BTYahoo emails. I recently had a problem with my BT Internet account and had to change the password. Ever since changing the password I can no longer receive BT Yahoo emails.

Obviously it stopped because of the password change however I could not find how to change the password in Google Mail on my phone I tried to re add the BT Internet Account but cannot work out how to do it.

Can someone help?