Hi Tammy,
You could try exporting all of your lead data for behavior, demographic, and person scores. Update Person Score in your spreadsheet so that it is equal to the sum of the behavior and demographic scores. Then import the sheet with the updated Person Scores.
Unfortunately, this isn't the most elegant solution as it does require using static exported data. There is a chance that someone's behavior or demographic score could change while you are exporting, summing, and importing. If that happens, you may have to repeat the process or make some manual adjustments. To minimize the chances of this happening, you should schedule this process for a time when the majority of your database is relatively inactive.
Moving forward, you could add a flow step to your scoring smart campaigns. Make sure that any change to Behavior Score and Demographic Scores also change Person Score by the same amount like so:

(Obviously, use tokens if possible)
This effectively ensures that your Person Score is equal to the sum of your Behavior and Demographic Scores.
Hope that helps!
Dan