Heading 1 is not appropriate for this use. It is a heading, not just some formatting.
Why use Microsoft Word’s built-in heading styles? by Shauna Kelly
I do not know if you did actually use Heading 1 style for this.
If you did, you can right-click on the Heading 1 in the Quick Styles Gallery on the Home tab and Modify it. Click on the Format button and then Font. Uncheck All Caps. Then save the modification.
You can also use Replace (Ctrl+H)
- In the Find box, click on the More button on the bottom and then on Formatting.
- Click Font and check All Caps. (You want to have it checked.)
- OK out of the Font dialog
- Click in the Replace with box and go back to the Font formatting dialog.
- Clear the All Caps box.
- Replace All

Note that this will change all ALL CAPS to not all caps.
If the typist used Title case when typing, it will change to Title Case.
If the typist did not, you may end up with all lower case or some mixture:
donald paul wisehart
Donald paul Wisehart
DONald paUl wiSehart
You can use Shift + F3 to do some shifting of case on selected text.
Anything more than this is going to require a macro.