Hi, I need help!

I have a table named TblMDR and a field named MDR.  I want
that field to automatically default to "BVL" and then an
autonumber.  I can do this in a query but it does not get
into the table and I need to export it into an excel
spreadsheet on a regular basis.
 
Example of the MDR field:

BVL1
BVL2
BVL3
BVL4
etc.

Thanks for help!

Denise