To fix white balance in a video, open it above, press Pick white (W) and click something in the frame that should be white or neutral grey, such as paper, a shirt, a wall or a cloud. Temperature and Tint are set to cancel the cast, and the whole clip follows. If nothing in the shot is neutral, Auto colour (A) estimates the balance from the frame as a whole instead.
The same two sliders work in the other direction too: move Temperature towards amber to warm a scene, or towards blue to cool it. For a styled result, the Warm and Cool categories in All looks hold ready-made looks such as Golden Hour and Nordic Blue. If the cast is part of a broader problem, start with color correction; for blue-green water, the underwater page is the better fit.