A practical way to clean this up in Bridge is to gather every image using the old italicized keyword, remove that keyword in one batch, then reassign the correct one.

Steps:

1. Search Bridge for the italicized/old keyword.
2. Select all matching images.
3. In the Keywords panel, untick the italicized keyword to remove it from the selected files.
4. With those images still selected, tick the correct keyword you want to keep.
5. After the files no longer use the old keyword, delete the italicized keyword from the Keywords panel.

Italicized keywords in Bridge usually indicate a keyword exists on some files but isn’t in the current master keyword structure the way you expect. The key is making sure all files using that old keyword are selected before removing it. This lets you fix the problem in batches instead of editing each image one by one.