how to remove/clear item from hidden purchases in the Mac App Store account.

What do yo mean? Do you want to un-hide a purchase that was previously hidden?

You can't. They were purchased.

Theony way wold be if Apple refunded your money for the pruchase.

It is to your benefit that it cannot be removed. You may, at some later date, want to reinstall the item. If it is still available in app store, you can re-doownload it.