View → Camera : set the current camera to the 3D view
View → Add Camera : add a new camera and set it to the 3D view
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Camera → View : Set the 3D view to the current camera
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Previous Camera : Use the previous camera (if multiple cameras set up)
Next Camera : Use the next camera (if multiple cameras set up)
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To install into Blender:

1. Download the .py file here
2. Blender → Preferences → Add-ons→ Install… Browse to and select the .py python file just downloaded , click the [Install Add-on] button bottom right and done!