You need something like this:
SELECT I.IssueDetailsId, I.ItemId, I.IssueWt, COALESCE(D.SumRWt, 0) AS ReceiveWt,
I.IssueWt - COALESCE(D.SumRWt, 0) AS BalaceWt
FROM IssueTbl AS I
LEFT JOIN
(
SELECT ItemId, SUM(ReceiveWt) AS SumRWt
FROM DetailsTbl
GROUP BY ItemId
) AS D
ON D.ItemId = I.ItemId;
SQL Server 2019 | db<>fiddle[
^]