1. Sign in at iris.fbr.gov.pk and start (or open) your return for the tax year.
2. On the "Summary of Economic Transactions" screen, scroll down to "Summary of Withholding Tax as Withholdee".
3. Click "Download Detailed Data" -- that saves an .xlsx file.
4. Attach that file here with the 📎 button, same as any other document.

Optional -- it just saves you describing each certificate one by one. You can skip this and tell me about your income directly instead.