Overdue Expense Receipts workflow

 Hi All,

I've a requirement to hide the 'Already sent receipts' button on Overdue Expense Receipts .I thought I amy able to personalize the embedded OA region to hide the "'Already sent receipts' " button. But, I 'am not able to locate the "'Already sent receipts' " button

Can you please provide some inputs on how this can be achieved. Any pointers on this will be immensely helpful.

Thanks

Manju