It sounds like the issue you're running into is that when LanSweeper scans, it sees all the fields it scans as dynamic. However, when you save something to any field, by default it's locked against scanning, as it was a custom value when updated.
Option 1:
Granted, this is not very great, and will require a lot of researching where things are in the database and requires you to have write access to the LanSweeper database. However, you can update the fields in the database directly by using an UPDATE query. So, for instance, if you wanted to allow the "Location" field to not be locked on all active assets:
UPDATE tblAssetCustom
Set LocationLock = 1 where
tblAssetCustom.State = 1
The issue is that the "lock against scanning" fields are strewn across multiple database tables, so it's hard to know which one the data is in, based on what you're importing.
Option 2:
Depending on how much you've onboarded into LanSweeper already, this could be an easy task, or make things much harder. My recommendation in your situation, since it seems like a new LanSweeper installation would be to delete the assets you imported previously, reimport your CSV in to LanSweeper only with the minimum fields required (see https://community.lansweeper.com/t5/managing-assets/import-assets-from-a-csv-file/ta-p/64312) and any other specific fields that you want to have not be overwritten by a scan, then scanning your entire environment to have LanSweeper pick up any dynamic fields from the assets.