Your WooCommerce Checkout Editor plugin that you forked from Woo’s own version (because I guess your theme isn’t compatible with it) has a pretty glaring bug I reported 9 months ago. In the time it takes to create a human being from scratch, the Pro team still hasn’t gotten around to fixing this…come on guys:
If you add a new “Select” field, once you click Manage options and enter/save all the available options, the link to Manage options vanishes and there is no way to edit them anymore. You have to delete the field and recreate it. Also the Placeholder field for this type of field is ignored and serves no purpose.