This MS site may help. Briefly, the key should have been automatically saved to your Microsoft account.
Hi Dell service team,   I purchased laptop dell inspiron model 5481 laptop , yesterday I formatted and installed OS after that my D and E drives are locked and asking for bitlock recovery key( 48 digits) I don’t have with me and I have used this is the outlook mail while I purchased my laptop  and I did not get any recovery code to this email as well, I have exam with  a week I have all details in my D and E drives . Please help me to provide the bitlock recovery key  . Please find the below details about my laptop
bitlocker recovery key request