Go to Service One and select SAP Access request(or follow this direct link)
After answering the questions according to your own situation, tick Production if you work on the usual mode and Pre-Production if you need to test developments before they move to Production
To get access to BW, the SAP system to select is WBP - BW Business Warehouse, then MD - Master Data Reporting in the Business Role
Complete the rest of the form with your specific details and submit
Don't forget to test your access once granted and revert, or answer any further questions the support may have to help you.