New field need to be added in ES55 transaction

Hi experts

1)I have to add new input field in transaction ES55( second screen where address and all other details are coming )to input Business Partener Number .

I tried to do so using user exit I tried all function modules of XES55 function group but couldnt find any exit.

What should I do?

2) My second requirement is as soon as user Input Business Partner No. the address details of that business partener should come here by itself as connection object address details.

Any ideas? What should I do?How can this be done.

Thanks