Use blue tape to tape around the outer frame, and tucking the edge where it meets the canvas. This will protect the outer frame from the paint, while you work on the project. Simply remove it when you’re all done.
This is much easier than it might look, and since your end goal is an abstract look, there is literally no way to mess this up. Simply squeeze several dobs of paint on the canvas as you go, and then lightly swipe the palette knife either horizontally or vertically, depending on your design, and make your way through the whole canvas, as you keep adding paint on in layers. Add more layers as needed after the initial one dries, if you’re still seeing any of the original design peeking through. Here are a few easy to follow DIY abstract painting videos, if you would like a detailed visual. (ONE, TWO) These really helped me to figure out how much if which paint to use and how to layer the paint.