Could you specify for what exactly you want to set username and password?
If you want to set login and password for SMS messages, so that login and password would be required for anyone trying to interact with device over SMS messages it would be like this: " setparam 3003:<Log in Value>;3004:<Your password>;"
Please note there are two blank spaces before setparam, because as of now you probably do not have set login and password. Once you have set it such command would look something like this: "<login><password>setparam 3003:<Log in Value>;3004:<Your password>;"
For more information about SMS commands and available parameters you can read in our Wiki at any of our product's SMS/GPRS command list and Parameter list pages.