If you are trying to restore eM CIient from an old computer as i suspect you might be doing, see @Gary post in the following thread.
All your previous eM CIient settings and accounts etc will then be identical on the new computer as it was using the backup & restore feature built in.
https://forum.emclient.com/t/transfer-em-from-one-pc-to-another/58064/9
However if you are doing a clean os install “on the same computer and not from another pc”, then make a manual backup via “Menu / Backup” (Pc) or “File / Backup” (Mac). You can see when the backup is complete in Show Operations via clicking the drop down on the right of Refresh top left.
Then copy the backup.zip file located in your “Documents / eM CIient” folder (by default) to an external or other drjve. Then after you reinstall your OS and reinstall eM CIient, put that backup.zip file back in the same folder. Then restore the backup in eM CIient via “Menu / File / Restore” (Pc) or “File / Restore” (Mac). It will then be identical again.