Getting information into the database is relatively easy.
Create your new field.
Export the files with the new field to a spreadsheet and add in the new data.
You need to have your fields in the spreadsheet match the fields in your db records. So, try to have the columns in your spreadsheet in the same order as those in your database. If you don't, that is not a big issue and can be worked around.
Once you have the spreadsheet, go to:
---- Import Records
and select the spreadsheet information you wish to import.
Match the fields you want to bring in, to the fields in your db. In your case, it will could be only the NEW field or if you delete the Found Set in your database you can import all the old data and the new new added field or fields at this time.
This is the general outline on how to do it. It is not complicated.
If the fields do not match, you can use your cursor to move the fields up and down until they do, make sure the arrow connects the fields before you press import.
If the first line of the spreadsheet has a header, check the box so you don't import that line.
Happy to guide you through it further if this isn't sufficient.