The Gallery Settings section in the Charitas theme Customizer contains 2 options. Navigate to Appearance → Customize → Theme Options → Gallery Settings to access these settings.

Options

• Gallery Custom Post Type (On/Off) — Enable or disable the Gallery post type.
• URL Rewrite Slug (Text) — Custom URL slug for gallery items.

After making changes, click Publish at the top of the Customizer to save your settings.