The other guy is right about letting the pan get hot first, but also remember that “hot” doesn’t mean on high, eggs like to be cooked low and slow. Just make sure that it’s actually up to that temp before you crack them in. Flick some water into the pan, if it sizzles for a second or two than that’s good enough for eggs imo (some will recommend waiting until the water drops hover, I feel like that’s too hot for eggs, but you know try both see what you like). I personally try to crack the eggs into the pan before the butter browns, but that’s just me. Another thing to be aware of that’s been mentioned in other threads under this post is that cast iron with a course surface can make things harder, so consider getting a smoother one or sanding yours down. Finally, for your best chance of getting under the egg cleanly, I recommend a thin metal spatula with some flex, like a fish spatula. In my experience plastic spatulas are culinary bulldozers. Be patient, if you think it’s close to done use the spatula to peak under the edge for a bit of a crust to separate from the pan, and if it’s ready, work around the edges to get it loose before you try to move or flip it.