Bad idea. I suggest you read the post on why relying on autonumbers is bad -
omissions in sequence.
You did not say where you wanted to start the autonumber. If you qant to
start at 50 then create an append query with two fields.
XX: 49 YY: "Test"
Set the ZZ to append to your autonumber field and YY to any text field.
Run the append query.