You can do butterfly if you can do breast stroke.
Try this, start with breast stroke swim and then slowly convert the components into butterfly.
So for example. Swimming breast stroke and then rather than returning your arms for the breast stroke pull, Fully bring the hands all the way to your hips like the butterfly swim..
Do that a whole lap over and over.
Then after you do that.. Repeat, but this time, after bringing the hands to your hips, bring them back right after you do it.. Make sure you YOUTUBE the proper form.
Then after you do that, switch it.
So this time swim breast stroke again, but leave the hands in breast stroke, but turn the kick to butterfly.
Then switch back again.
Breaststroke kick, butterfly hands.
When you got the arms strong enough, which you probably already do got.
Then you can convert both into butterfly.
The trick to doing proper butterfly is your head lead.. Don't rush your arms. Make sure you do the head first thing. Do youtube to figure out what that means.
Bob bowman says it about Michael Phelps' swim, THE HEAD LEADS THE HANDS.
Head up before arms out the water.
Head down before arms enter the water.