Originally Posted by
chrisleusa
Can you please let me know the name of this cassette so I can look up the tool and how to open it?

Thats a SunTour freewheel which takes a two notch remover. Park tools version works well. FR-2.
…as it is a freewheel it comes off as a unit.
1. Remove QR skewer
2. place tool in the notches completely
3. put skewer back on and tighten until the springs compress against the tool
4. place wrench/adjustable wrench on flats and pray it turns counterclockwise easily. If not, Kroil from the back!