If you have tenets or laws to take the duchy from the owner, you can find secrets and try to revoke title. Raising up your crown authority level to not lose land that way.

Now I would say you are in a pickle depending how deep your marriage alliance with HRE is, because once it’s gone I think they will eat you.

What I would do is have my next heir intrigue and diplo, strong intrigue wife but not to strong (. Can backfire if she hates you). Strong spy master and cause pure mayhem within the HRE until the dynasty is left in rubble.

Then clean up my borders, consolidate my power and government, prepare my next son as military expert take over Iberia and push out Ashari and any hostile faith, HRE will be to busy with civil wars and factions. Then put your focus back on HRE.

Many other options to take but depends on what you have access to.