You can not delete the records while importing, but what you can do is do the lookup in Excel and add a column "Active" to your spreadsheet. For the incorrect/duplicate records set this to false. When you import the file these records will be archived in Odoo and you won't see them again unless you specifically search for archived contacts.
If you really want to delete the records, you could overwrite the name of the contact in Excel to, for example, "Delete 1", "Delete 2", etc. Import the file and then search in Odoo in Contacts app for "Delete", select all records in list view and click Action > Delete.
When you export the contacts from Odoo make sure you have selected "i want to update data" so that the first column contains the external ID of the record in Odoo. If you then import the data, the existing records will be overwritten.
I made a custom field on the list view of contacts with created on date, then created custom filter for created on date and deleted them by multiselect checkbox. You need studio for this method.