For that someone (who you authorize) need to make an online HEC degree attestation account (as they send text to confirm )and fill in all your details.
1.If you have IBCC attested SSC and HSSC all you need to do is pull your details in online HEC account.Otherwise get your SSC and HSSC attested from IBCC
2.When HEC is done checking your documents they will ask about date of your choosing for attestation.
3 Send someone with your CNIC copy to HEC office in Islamabad (if they can) or regional office,or They can send your documents through designated courier company for attestation,they will do attestation process and return back to your home address.I am not sure if this service is asked in your online profile,but i guess i have seen one.You have to request them to seal the Color copies.
Edit :
http://hec.gov.pk/english/services/students/Degree Attestation System/Pages/Degree-Attestation.aspx
Check this weblink ,this might help.