Without seeing the footage
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Without seeing the footage, there is only so much I can suggest. What you should first aim to do is brighten the video using your color correction or luma correction tools. You’ll notice that the image will probably wash out, and the noise level will increase. You can regain some color fidelity with the saturation control, but noise is much more difficult to remove. There are plugins like Neat Video’s Noise reducer that will help reduce noise.
Just like dealing with a thin film negative…there is only so much you’ll be able to ‘fix’.
Perhaps you can post the footage up on Vimeo in a high-quality H264 compression, and allow us to download it in an attempt to help.