how to clear all invoices and receipts from existing account at once.
I would like remove all things and set to zero.
@Zishan_Rana, there is no way to remove everything with one action. Manager will not allow you to delete records already referenced by other transactions. So, for example, if a sales invoice has been settled by a receipt, you must delete the receipt first. Then you can delete the invoice.
It would be nice to have a button that clears all transactions at once.
Think about how easy that would make it to accidentally destroy the records of a company.
True but we already have a button that can destroy all records here:

My idea was to modify this button to allow deleting only transactions from specific or all tab/s.
Remove Business does not destroy anything. It takes a business off the list. The complete daya file remains in the application data folder.
Does that mean Manager keeps user data even after removing the business?
Yes. Read the Guide. A removed business can be brought back.
Remove ≠Delete. Removed businesses go to Manager’s Trash folder.