Monica, moving one of the budgies to a separate cage is a good idea. Great that you recognized the need for it
. Later on, you can try them together again, if the cage is at least 30”x18x18.
If the style of your cages allows this... open both cage doors and hold (or temporarily tie) the cages tight together at the door openings, to allow one to pass through. This might take some time, but you can encourage the passage through with an enticing sprig of millet. You can also put the food dishes in the other cage just inside the door, so they’d have to go in to get it. Just make sure both don’t go in!
Or you can catch one. It makes it a bit easier to catch a wild bird when the lighting in the room is dimmed. If you can turn down a light, or pull the shades. Go in calmly and slowly. I know the birds are fast; but with a small cloth that is big enough it will give your hand more surface area. You might want to pause a couple times to see where they are and get at a good angle. Only move your hand fast when the cloth is closer to the bird. In other words, don’t spastically chase them around the entire cage.
You might want to remove excess branches or toys that might make it harder for you to catch one, if you do that method.
Good luck, Let us know when you’ve accomplished this