The contents in the document are shown in the figure below.

Method 1:

Select the text set to "Title I". If there is more than one text, you can hold down the Ctrl key to select more than one text, and then click "Title I" in the Start tab.

Method 2:

(1) Click the Outline button in the View tab.

(2) Select the text set as "Title II" (Level 2). If there are more than one, you can hold down the Ctrl key to select more than one, and then select "Level 2" in the outline tab (as shown in the figure below).

(3) You can use the method (2) to select the text set as "Title III" (the third level). If there are more than one, you can hold down the Ctrl key to select more than one, and then select "Level 3" in the outline tab (as shown in the figure below).

(3) Click the Outline tab Close to return to the normal view.

④ The effect is shown in the following figure.

Note: Using the second method to add the title level, you can set the font and font size according to the actual situation.