Delete all directories, and then "insert"-> "citation"->; Indexes and Directories, and then open the Indexes and Directories dialog box. Don't confirm it yet. Watch the modify button carefully. Click Modify to open the Style dialog box. You can see the index 1, index 2 ... index 3 .................. selection indicator 1, and click Modify to open the dialog box for modifying styles, with a format button in the lower right corner. Click Modify. The update directory will not change. If the topic of your thesis is level 3, you can change it to a level 3 indicator. Similarly, the title of the second level will be changed to index 2, and the latter will be ignored. Just making sure.