Submit Purge : one Operating Units

When in AP I'm running the Purge application, it opens up the Submit Purge screen, which allows to enter the parameters for purge.

In the first field, it's stating the Operating Unit. But, when you look at the value, there's in fact only one of them.

Obviously, this is where one should select different values.

How can I select other values ?

I'm using the Payables Purge responsibility.

Thanks