I use a finger rather than a screw driver.
This is the hook bracket. Using a slot head screw driver unlock the shade at the back with a slight twist. The shade will install using the revers method. Hook the shade at the front and rotate backward till you hear a "click".
2 Cord Shade have 2 brackets
4 Cord Shade Normally have 3
Left is the hook bracket
Right is the lip bracket
Normally this is used to center the shade before 2 screws are installed.
The screws are normally Phillips Head screws (Star head).
They are approx. 1/2 inch from the ends of the shade and are installed directly through the shade into the valance box. These are plastic and do not flex. Just pull froward on the head-rail after screws are removed.