That is fairly simple to do, but it's best not to do it in the way you think.
Because Form1 is the parent of both Form2 and Form3, it should be the only form which konws about them both - otherwise, the design of all three forms is locked together, and it becomes a lot harder to maintain them.
So what you do is to create an event in Form2 (call it ShowDetailsRequest or similar) which is Handled in Form1. The event handler than opens Form3 (or not, if it has a different way to display the information) after getting what information it needs from Form2 via public properties.
This is really easy to do: have a look here A simple code snippet to add an event
] - the code you need is in the top of the Tip, the rest just describes how to make it easier to create them.