The easiest way to start is to put the cursor inside a style. Here, it is the fourth level of argument headings.

(It is probably not a good idea to have so many levels, but five are available in WordPerfect. More could be created with custom styles.)

Using the menu, click Format | Styles ...

(I prefer the keystroke Alt+F8 instead.)

You get the Style list box, which lists all active styles. If the cursor is within a style, that style is selected. Here it is "Level 4."

Click the Edit button to see its coding.

This shows the codes that make up the Level 4 style. The factory setting for Level 4 consists of three [Hd Left Ind] (indent) codes, the [Para Num] code, and another [Hd Left Ind] code.

I have modified those settings in this appellate brief by:
1. Replacing the last indent code with a space (for aesthetics);
2. Applying Table of Contents Level 4 to the number and text (so that this heading will appear in the Table of Contents);
3. Placing all of that in bold codes (so that bold codes are not generated in the Table of Contents);
4. Preceding all of that with the single space code (to alter the double-spacing of normal text for this heading); and
5. Adding a hard return at the end (to get the normal separation between the heading and text that follows it).

Similar changes were made in the other Level Styles.