The simplest way is to use (for the first time):
INSERT INTO [destination database].[dbo].[destination table] ([destination field1], [destination field12], [destination fieldN])
SELECT ([source field1], [source field12], [source fieldN])
FROM [source database].[dbo].[source table]
Next time, you'll need to use
UPDATE[
^] statement.
More:
INSERT Examples (Transact-SQL)[
^]
SELECT statement (T-SQL)[
^]