I presume the brows are a prop? Correct? I suspect there's actually two morphs present in the brows. Either way the fix when you need to update a morph from zbrush

Poser doesn't have a direct "Update this morph" thing but it's easy to do

• Goz with the morph dialed
• Fix in zbrush
• Goz back to poser
• Let poser create a new morph
• Make sure only your original morph and the fix are dialed to 1
• Object > Spawn Morph Target ... (Of Figure > Spawn FBM ... )
• Now you can delete both the original and fix morphs.

This combines the original and the fix into a new morph. Before you combine them you can adjust the blend of the fix and the original by trying various combinations of dial spins on the two morphs. I find my self sometimes over fixing and morph. If your do that just spin it's dial to less than 1 when you're ready to recombine them.

You can also brew up experimental fixes. See how they look together and only combine the ones you like. or, and mixture of them.