Assuming you are on a fairly recent version of macOS, connect the drive and go to Applications > Utilities > Disk Utility
In the sidebar select that drive and then at the top click on the "erase"button. In the resulting dialog, give it a suitable Name.
Select the Format as APFS (hence my assumption above). Then select the Scheme as "Guid Partition Map" and then click on the "Erase" button at lower right. When it tells you it is done you can quit Disk Utility and eject or use the drive for your CCC backups.
If you are still on an version of macOS where the APFS Format is not appropriate, use "Mac OS Extended (Journaled)" instead for the Format. But if you are that far behind in your version of macOS, it really is time to update the OS ! (i.e Mohave or even earlier in some instances).