Let's see how this can be done by using the multi-select option:
1. At the top of your Dashboard page, hover your mouse over the Audience tab to reveal the drop-down menu and then click on the Email lists option.
2. Click on the name of the email list from which you want to copy members to another list.
3. Click on the View all members tab, to view all the members contained in your selected list.
4. Select the members that you wish to copy to another list, by checking the box on the left of their Email.
5. Then, click on the Select action field, located above your members' list, to expand its menu.
6. In the drop-down menu that appears, click on the Copy members to another list option.
7. In the pop-up window that appears, use the drop-down menu to specify which list you want your selected members to be copied into.
8. Check the box next to the Merge Custom Fields option, if you wish the custom fields from the two email lists to be merged. Please keep in mind that this option will import the custom fields contained in the list you are copying the members from, not in the one that your subscribers will be copied.
9. If you have the double-opt-in consent from an external source, click on the check-box Yes, add the members as verified, I do have consent in order to add the members as verified.
10. Once you are satisfied with your setup, click on the Copy to list button to complete the process.
A pop-up message will appear at the bottom of your page, informing you of the successful completion of the copying process.