As we explained when looking at importing products, once you have defined fields in Sales Layer and established associations between fields and columns when importing, the system will remember them for future imports.
Nevertheless, the situation could arise where you want to restart the account in such a way that no products or configuration data from previous fields are kept.
To do this, first remove all the products (otherwise you will not see the following option), and go to Actions> Edit Forms:
And from there Actions > Restart Table.
Once this is done, when you next go to import data into Sales Layer, it will not remember previous import fields but will start over from scratch.