Hi adzuki2812,
Thanks for reaching to us.
The Negative Sign by default appears on the Sale Label to depict the amount of Sale Percentage being offered on the Product. This is how by default it appears on WooCommerce end and there is no option in Theme Settings available to change or hide that. It requires Customization and this is beyond our limitations and support policy scope. Hope you can understand our limitations.
We would suggest you to try consulting with WooCommerce Support in this regard, hopefully they can guide you better with this.
Regards,