In the editor, click on 'Expr-reqs' to add prerequisite expressions.
Code:
#trait[attrSma] >= 3
#trait[attrAgi] >= 4
Those should be the expressions you'll need. Look at other Edges that have pre-requisites for examples of code. And remember that in the Savage Worlds data files, Attributes and skills are stored as half their die value (D4 is 2, etc).
Don't forget to put in error messages.