Hello @magento
Welcome to the Forum, and thanks for reaching out to us.
There is no Duplicate button or icon to duplicate slices. But you can duplicate or add the same slice from your repository. For this, go to your custom type, click on add a slice icon, and a pop-up will open where all the created slices are available. (Screenshot attached).
Let me know if you need any further assistance.
Thanks,
Priyanka