You need to start with scanning the computer for codes but I'm going to guess that the plugs are fouled out from the oil. This will require a complete inspection for a proper diagnosis. If you don't work on your own car the use this link to find a good shop near you.
https://repairpal.com/repair-shops
Alex
RepairPal Certified shops can diagnose and repair your 2011 BMW 550i. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
