Use a small screwdriver.
1. Open the clasp with the logo on
2. Open the clasp without the logo on
4. Open the next one
7. Place a small screwdriver in the slot where the arrow is and lever the screwdriver gently towards the watch face
9. You may need some force when adjusting the strap
10. Align the slider to engraved level. Put on your wrist and adjust to suit
11. Press down with your finger