Type this EQ \o(ˆ,p) Select what you just typed, press Ctrl+F9 to make a field out of it, and press Alt+F9 to switch between display of field codes and field results. You make the ˆ by pressing Alt+0136 (that is, press and hold the Alt key, and type the numbers 0136 from your numeric keypad, not the number
keys on the top row of your keyboard). Looks okay with a lower-case p, but not so good with an upper-case P.

If you need a hat over an upper-case P, then you can type Pˆ and then experiment with multiple Advance fields to move the hat to the left and above the P and then move the cursor back to a normal position after the hat. In 12-point Times New Roman, you might try P{ ADVANCE \l 5 \u 3 }ˆ{ ADVANCE \r 1 \d 3 }

If you often use this symbol, you can create an autotext or autocorrect entry for it.

via Putting a hat over a consonant – Microsoft Office Word.