DELETE aa
FROM aa
INNER JOIN bb
ON bb.ID = aa.ID
SET IDENTITY_INSERT aa ON
INSERT INTO aa (Id,Policynumber,date)
SELECT Id,Policynumber,date
FROM bb
SET IDENTITY_INSERT aa OFF
For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden