Sorry, now I only understood your exact problem. Please try the following solution:
Right-click the date field in Word and select Edit Field Option. Then, click the Field code button located at the bottom left of the dialog box. It may show a field code string in a box like "MERGEFIELD Date."
In my Excel sheet, I used the field name "Date." In your system, it may be different. Insert the text below after Date: @ "MMMM, DD, YYYY"
The final field should be "MERGEFIELD Date @ "MMMM, DD, YYYY""
Now, click the OK button and check the output.