1. On the File menu, click Open.
2. In the Look in box, click the following folder:
C:\Program Files\Common Files\Microsoft Shared\Proof
3. In the Files of type box, click All Files (*.*).
4. Click the Custom.dic file, and then click Open.
5. Delete any words you want to remove from the custom dictionary.
NOTE: Be sure to delete any blank lines left after you delete the words.
6. On the File menu, click Save As.
7. In the Save as type box, click Text File (*.txt; *.csv).
8. In the Look in box, click the following folder:
C:\Program Files\Common Files\Microsoft Shared\Proof
9. In the File name box, type Custom.dic, and then click Save.
NOTE: Do not edit the Custom.dic file to add words to the custom dictionary.
The words in this file must be sorted in ASCII alphabetical order.
https://www.pcreview.co.uk/threads/microsoft-works-dictionary.2241290/