When you state PIVA I'm assuming you mean PVA or Postponed Vat Accounting.
PVA is a system which allows you to help with cash flow on your imports by not paying any VAT when the goods are imported in to the UK.
Instead of paying the import VAT and reclaiming it on a UK VAT return PVA allows you to not pay the VAT but just to record the import on your VAT return.
Please see the guidance below which explains how PIVA works and how you would complete your VAT return.
Check when you can account for import VAT on your VAT Return