Navigate to the img2img tab in the Forge web UI.
Drag/Upload an image that contains generation metadata onto one of the main canvases (e.g., the img2img or Inpaint tabs).
The "Extracted Prompt" textbox in the helper will populate with the prompt from the image.
Use the "Remove" and "Add" textboxes to prepare your changes.
Click Apply Modified Prompt, Apply Seed, or Apply Neg Prompt to send the data to the main UI fields.
Alternatively, you can auto-apply the prompt and/or seed when uploading an image