Global Account mapping is used where the transaction sets the account to be posted to . If the transaction Gl impact is not affeced through an item involved or if a transaction doesn’t contain an item and in these scenarion we can change the GL impacts according the accounting book.
One Journal entry 2 different Gl Impacts in 2 accounting books
Setup> Accounting > Global account mapping

Provide details like subsidiary, effective from, source account and destination account

Create a transaction and Check the GL impact
Result:
