The SAP report S_ALR_87013340 is a standard report used for displaying the “List of Customer Open Items”. It is commonly used in SAP Financial Accounting (FI) modules to provide an overview of open items related to customers.
As the first step, you should look for possible enhancement points in the code of the standard report. If you find a suitable enhancement point, you can use it for your customizations.
If there are no suitable enhancement points, you can also create a custom report that will replicate functionality of the standard report but with required customizations. This is going to be a higher effort approach.