The process is very simple, but useually people don't want to goto government offices.
They want the person on who's name the order is and a copy of his ID card.
Just visig GOP lahore office along with ID, you will find alot of clerks outside, show them the notice you got and they will fill a form for you for 50Rs. Take the form to inspectors office, he will then sign on it and then ask you to goto the international post office block which is at back side, those guys will find your parcel(This is where you will see these guys looting people's parcels) you have to get your form singed from these guys, they will also attach some additional forms with it and then ask you to take it back to the head inspectors office, where he will ask you what exactly the product is and if there is any duty on it. This was an old punjabi baba, and he though just because my product has wifi its a mobile, I explained him, and even showed him my aliexpress order that it's not a mobile and just a scanner. And then he said okey there won't be any duty and then signed these documents, and then you have to take these documents back to the ipo office where they will take the form but won't give you the parcel and tell you that they will deliver it. Pm me if you need any help.