Spoiler alert - I have the solution underneath this text, click and highlight if you want to cheat, move along if you want to figure it out on your own.
Imagine the rocks are numbered 1-7 from left to right.
Now click on the following sequence of numbered rocks: 3,5,6,4,2,1,3,5,7,6,4,2,3,5,4 - your frogs are swapped!