Never mind. I finally figured it out after I look into the rb code. I just use the scale tool and type in a ratio = square root of (new area/old area).

Thanks TIG. It's a very useful tool. Is there a way to scale the other faces with the same ratio? The plugin only scale the selected face, but the remaining faces remain unchanged as shown below:

Please let me know. Thank you so much again!

Best regards,
Leo