Edit a single alphabetical index entry

I’m wrinting a book, and I have already set many names as alphabetical index entry, but in a manner I now wish change (adding the person’s prenom, the given name, as well and not only family name).
So far I didn’t manage to find how to do, unless deleting that entry, what in case of many occurencies is quite boring.
There is another way to edit a single alphabetical index entry, withoit deleting it?

present state: Hegel
what I wish: Hegel, Georg Friedrich Wilhelm

Edit your question to give a concrete example of the present state of a sequence containing an entry and how you want to change it.

Thanks for the edit but I wanted it more detailed, such as (arbitrary markup to hint your real formatting):

blah, blah, <index entry="Hegel">Hegel</index> was a German philosopher. blah! blah!

where “entry” is to be changed to “Hegel, Georg …”.

Is this your goal with a change at every entry?

Yes every entry of a certain name. In the text there is not what I want add (the given name), there is only Hegel, not Georg Wilhelm…
I noticed that when I add a new entry name, I can add also another word.
But I didn’t know when I started with the entries.

When editing “complex” documents (adding index entries make a document “complex” for this question), always work with View>Formattings Marks and View>Field Shadings enabled so that you can see where hidden formatting/markup is located.

Indexed words have a light gray background. Hover your mouse over it. A tooltip appears displaying the index entry. Right-click and Index Entry to edit.

Warning! If spelling checker is active and the word under the shading is underlined with a red wavy line (denoting a spelling error), the pop-up menu does not offer Index Entry. So, fix the spelling mistake first or disable spell check.

The Edit Index Entry dialog allows you to modify your entry. You can also navigate from entry to entry (without the need to hunt for them) with the solid black arrows above the buttons.

Thanks to the navigation arrows, it does not real matter which index entry you select to begin reviewing your document.

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In case you need clarification, edit your question (not an answer which is reserved for solutions) or comment the relevant answer.

Thank you. Your solution works, even in my opinion LO should provide a faster one (like any other search and replace).