You speak with the staff member who was going to issue you the refund. If the staff member is not able to give you the item back, he will tell you to make a refund request as long as the requirements are met. You can read more about refunds here.
Look, as I said, you can only ask for refunds if the item was lost due to a rule break or bug. Once that is confirmed by reporting the said player and they are punished, or your bug report is accepted, the staff member who handled the situation will tell you how to make a refund request. You can also use this guide for more help. https://help.perpheads.com/page/refund-requests
If you lost something (in total over 5k) to a rule break you can make an action request on the person here https://perpheads.com/forums/action-requests.31/ and the admin handling it can authorise you to make a refund request if its confirmed a rule break occured. (if you look at rado's message you can find out where to make one) If they were already punished then I would contact the admin who handled the situation to inquire about it. If you lost it to a bug then select Bug report as your evidence type and provide that there.