Hi! I assume you credited the Avios from that flight to your Iberia Plus account?
If that's the case, you should be able to transfer the Avios from Iberia Plus into your British Airways Executive Club account (you may need to open one first). Then, you can transfer those Avios from British Airways Executive Club into your Qatar Airways Privilege Club account. Those transfers are free and take place at a 1:1 conversion rate - just make sure the name on each of your accounts (Iberia, British Airways and Qatar) matches exactly (including middle names).
This article explains a bit more about this process:
Avios is the common points currency of five airlines: British Airways, Iberia, Qatar Airways, Aer Lingus and Vueling. These diagrams show which frequent flyer programs you can transfer Avios between, and which airlines partner with each program.
www.australianfrequentflyer.com.au
That said, since both Iberia and Qatar Airways are in the Oneworld alliance, you can credit Iberia flights directly to your Qatar Airways account and earn Qatar Avios that way. You can also redeem Iberia Plus Avios to book Qatar flights. So you might not need to go through the hassle of transferring your Avios, depending on what you want to do with them.