Document Splitting-Activation

Dear Experts,

We have one company code activated document splitting but another company code not yet be activate till now.

They wants activate a document splitting at the beginning of the financial year.

I found some notes which is provided by the SAP the below mentioned points needs to be followed.

All the open items must be cleared

We have a 10500 open items for G/Ls , 12000 for vendors & customer 10000 open items.

How to clear the open items and how to upload again.

Please provide a correct solutions for the activities.

This is SAP ECC environment