This sounds like a pos that should have been entered in the FM PRo forum. Report an Issue is intended for reporting possible bug in the software. Poste made to the FM Pro Forum (see tabs at top of this screen), will be seen by a great many more people so you can get help from more of them there.
A group records (38) from one specific field has been auto populated or overwritten with the note information from one of 38 entries.
Make sure that this data is in a field that is part of the record that you think that it is a part of. It's possible that all 38 records link to the same record in a related table and this field is displaying data from that one related records. It's also possible that you have 38 records that all store data that has been overwritten like you describe. It will look the same on your screen, but how you resolve the issue will be different.
If you have 38 records that all store incorrect data, this cannot be undone. You can either use Replace Field Contents to change the data back (Make sure that you have just these 38 records by themselves in your found set) or you may have a back up file where this data is still correct and then you could import the data from the back up file. This might be done as an "update" import or you may have to delete the 38 records from your table, pull up the 38 records in your back up file and then import them.
All of this should be done with care--deleting records in one table can delete related records in other tables if that option was specified and Replace Field Contents operations cannot be undone. It will be a very good idea to make back up copies before you make changes to the file where you are trying to resolve this issue.
how can I ensure that this does not happen again?
You'll need to figure out how it happened in the first place before you can devise methods that will prevent it. Much depends on the design of your database--the tables, relationships, layouts, etc. And regular backups of your data are essential to help recover from user errors of this type.