How to remove grains from DSLR footage?

I have a Nikon D3200, and I've been using it for about a year now, but no matter where I'm, if there's a lot of light or less light, my footage is always grainy. I gave it to the service store, but they can't find any problems with it. I'm starting to think maybe I don't set my camera settings right. Could I get some tips on how to remove grains, when shooting in a low-light atmosphere?

It's not grain, it's digital noise.

Use a lower ISO setting. Lower ISO = Lower Noise

In low light situations you might have no other option than to increase the ISO, which will cause noise. Your video editing software might have noise reduction you could apply.

Less light means higher ISO. Higher ISO means less details & more grain.

You can go into manual mode to set the ISO, but now your shutter speed has to be SLOW to get more light into the camera. Can you stop your heart-beat for a second or so to reduce camera shake?

Or - use a tripod.

Or - do what every other photographer does: improve the light.

Set the ISO to 200.

When you say you are getting "grain" in your "footage", I have to assume that you are shooting video. Just so you know, grain is an attribute of film. What you are seeing is noise

With video, the shutter speed is constant based upon the frame rate of the video.

What that means is that the only variables are the lenses aperture and ISO.

Once your lenses aperture is wide open, the camera will automatically increase to assure a good exposure, but in doing so, you will begin to see more and more noise

What your eyes see as "lot of light" is not really.

One of the issues facing people new to shooting video is that you have to add light to any indoor scene to increase the light level to reduce noise caused by the camera using high ISO settings. If you replace the existing light bulbs with 500 watt lamps, there will be less noise in your videos.

"Footage" - do you mean movie clips or are you asking about still photos?

In any low-light situation, especially for movie work, there's a tendency towards graininess. Editing software can to some extent help but you will always have the probability of grain appearing when shooting in low light levels - that is a "fact of life". If you spend a lot more money than the D3200 costs you can buy DSLR bodies which are better in low light. But I do mean "a lot more money".

Set ISO to lowest.

In video all camera functions go to full auto. The camera decides everything except focus (if you use manual focus which you should) and the shots themselves.

If there's grain that's because the camera is trying to compensate for the lack of light. You need to shoot in better lit areas to get better results. Trust me, it's not the camera, it's you.