The Stories plugin has the option to submit stories from custom page. Here’s how you can set this up:

1. Create a page and add the shortcode [um_story_form]
2. Go to WP Admin > Stories > Settings
   
   1. Under the setting “Form Page”, select the page created in step 1
3. If you would like users to stay on the form page after submission, change the field “Save Redirection”