UPDATE jr
SET jr.SavedTransactionId = t.Id
FROM dbo.JournalRequests jr
JOIN dbo.Transactions t ON jr.Id = t.JournalRequestId;

Then to catch the rest:
UPDATE JR
SET JR.SavedTransactionId = TSE.TransactionId
FROM dbo.JournalRequests JR
JOIN dbo.TransactionStatusEvents TSE
ON TSE.EventDetails LIKE '%' + CAST(JR.RequestId AS NVARCHAR(36)) + '%'
WHERE JR.SavedTransactionId IS NULL;

Close #443 But need to run update scripts above in order.

Didn't test, but code looks okay. Is there a reason you didn't include those UPDATE queries in the migration? It's pretty easy to do via migrationBuilder.Sql().

Was just going to manually do it after.