Contacts incorrecly imported from Thunderbird

I imported everything from Thunderbird but have found that Contacts have been incorrectly imported. Names appear in the File as column, not in the Name column. How do I copy/move them en block rather than individually? There are too many to copy/move individually.

Hello Ian,

We’re sorry for the inconvenience. Could you please try manually exporting the contacts from Thunderbird into .vcf or .csv and import them through Menu -> File ->Import… - the relevant contact format?

Thank you,
Maurice

Hello Maurice,

Thanks for your reply.  I have exported the Address book in CSV format.  You ask me to import them through Menu -> File ->Import… - the relevant contact format, which I take to mean either .vcf or .csv.  How do I find the correct headings?

Thunderbird gives:
First Name, Last Name, Display Name, Nickname, Primary Email, Secondary Email, Screen Name, Work Phone, Home Phone, Fax Number, Pager Number, Mobile Number, Home Address

Whereas all I can see from column headings in the Address Book - Local Folder window are the following: 
Full Name, File As, Job Title, Company, Category, Mobile Phone,  Work Phone, Home Phone, Email

My Thunderbird Address book did have names in the First Name, Last Name, columns, whereas eM Client only has full name.  Is that why the import failed?

I can concatenate First Name, Last Name into a new Full Name, and delete and rearrange columns to correspond with the eM column order, if I know it.  Please confirm that the above is correct or send me the correct  eM column order.

If I simply import the new contact data as described above I am going to end up with a lot of duplicate entries.  How do I delete the duplicates in bulk (not one by one I have too many)?

Alternatively, can I just delete part of the Address where no names have been put into the Full name column, or do I have to delete the whole address book and start from scratch?

Either way, how do I make a backup up the existing eM Address book first, in case I make a mistake?
I look forward to receiving your suggestions before I start this process.

Best wishes.

Ian Williamson