If you want to make a segment, but not sure how to filter out just the contacts you need, you can add a new value just for this purpose.
This can be useful, for example, if you want to filter just the contacts starting with a particular letter.
If you have your list outside Mailigen platform, just add a new column and create a new easily distinguishable value, for example, “1” and import these details using “update existing subscriber details” option. Follow the steps in this video
After you have added the new value, creating a segment should be easy.
Follow the steps in this video