First, highlight all entries and delete them.

Now, there are two choices. Pick whichever works for you.

The CSV approach

1. enter one good email address with fields you normally use into thunderbird's addressbook
2. click the three dots to the right of addressbook name and export in csv format. This will be your template
3. open that export into a spreadsheet program
4. note the top row. this shows the columns as thunderbird expects them to be
5. open your exported outlook csv into spreadsheet and adjust columns to match, including the top row.
6. save as csv
7. import into thunderbird

OR

The Thunderbird import approach Use the Thunderbird import for CSV at tools>import>import from a file if a screen opens to show selected fields for the import, this happens because Thunderbird senses that mapping is needed. (see attached)

1. untick the fields that are either incorrect or not desired for the import
2. next, use the drop-down menu on each desired incorrect mapping and select the appropriate entry. For example, in the attached screenshot, the Nickname is incorrectly assigned to Title, and the true nickname is assigned as Secondary Email. Resolving this is a simple as clicking the drop-down menu and selecting the Nickname option.
3. once all corrections are done, click the submit button.

rancher4951, did this work for you?