You want to edit a G/L Account.
There are 2 ways to Edit the G/L account. One is through SSCUI 150001 and the other is via App 'Manage G/L account Master Data'.
You need to enter the Edit mode and make your changes.
If the account still has postings (the balance is not zero) than the Open Item Management settings cannot be changed.
You need to clear all your postings in the proper G/L account in order to be able to change this customizing.
Note that for the Manage G/L account Master Data app you have to set all the permissions to your CBuser as 'Unrestricted'.
Also, you can try the Manage G/L Account Master Data (Version 2)
2740067 - Best Practice J58 - Accounting and Financial Close
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