basically, don't use a
static
method. You need an instance of a form, make the method a member of that form and use the instance that provides.
If you are trying to do this from a different form then you shouldn't - you are making that for (or static code) far, far too aware of the mechanics of how Form1 works, and that's a very bad idea.
Instead, you should be using events to get Form1 to deal with it itself (if it chooses to). That way, OOPs is satified and your code becomes a lot more maintainable.
Exactly how depends on the "relationship" between the two forms.
Have a look at these, one of them will fit your circumstances.
The form that creates an instance of another:
MyForm mf = new MyForm();
mf.Show();
Is the "parent", the other form is the "child".
(This doesn't imply any formal MDI relationship)
Transferring information between two forms, Part 1: Parent to Child[
^]
Transferring information between two forms, Part 2: Child to Parent[
^]
Transferring information between two forms, Part 3: Child to Child[
^]