How does one change the level of a ToC entry without adding a duplicate ToC entry?

Another user added ToC (Table of Contents) entries as level 1, but they needed to be level 2. There are quite a number of them. How can one change the level without adding new entries?

Use the Navigator (F5).

All headings are under the Headings section as on can expect.

Unfortunately you can’t process all levels 1 simultaneously. Select a level 1 heading you want to fix. Click on the Demote level icon in the navigator toolbar (the one with a single horizontal triangle pointing rightward). This will change Heading 1 paragraph style to Heading 2 and also all subordinate levels will be incremented so that the outline relationship is still respected. Repeat for all other level 1 to be fixed.

Note: if you want only to change level 1 to level 2 without changing depending level 2+ to level 3+ you must do that manually on each paragraph setting its style to Heading 2.

If this answer helped you, please accept it by clicking the check mark :heavy_check_mark: to the left and, karma permitting, upvote it. If this resolves your problem, close the question, that will help other people with the same question.