Your aim is to grip the top of the cover with both hands using thumb and finger(s)

You need to pull the cover up to the fixed plastic casing (with the force required the plastic casing bends but did not break)

While pulling upwards, you need to be pulling towards your body and using your little fingers pushing outwards on the sides of the printhead tray carrier while tilting the cover

You may hear creaking of the plastics, but with patience and firm but gentle persuasion you should end up with the top of the plastic cover sat on the fixed case (Image 1)

You need to then work the sides out carefully (Image 2) using the flat bladed screw driver for assistance if required while pulling up so the tabs don't get snapped at the bottom of the part

If successful, you will have the cover off (Image 3)

Note the tabs (Image 3 red arrows) and the best spots to place your thumbs/fingers (Image 3 green arrows)