I assume you followed the standard procedure of Writer when you created your Index entries and your Index table. If so then you can do:
- Open the Styles and Formatting window (e.g via F11)
- Click the tab paragraphs - this typically the default
- Place the cursor in the title of your index table.
- Look into the paragraph styles and now “Index Heading” should have a grey background
- If you don’t see any entry with a grey background go to the bottom of the window and select “All Styles”
When have created your index table in the standard procedure you should now see “Index Heading” with a grey background
- Right click > modify > font tab and change here the font etc you want to use
- Click “Apply” and the “title line” of your index table will show the new font you selected.
- Click “Save”
If this doesn’t answer your question, please explain in details how you created your index table.
Two side notes:
1 -When you want to make a text line a heading 1,2,3, etc you do not need to select the entire line, you only need to place the cursor in this line and then do ctrl+1 or 2 or 3 etc and you created the heading 1, or 2, or 3, etc
2 - Make a daily backup of your book thus a loss is maximum 24 h of work
And make sure a copy of the backup is on an external drive. Ideally have 2 external backups. Store one even outside your house. I did this with a similar work and then slept very well.
(I added the side note 2 because very often the question “How can I get my file back…” appears in this forum.)