Epson H6000III - TM Two-color Thermal Line Technical Reference Manual page 72

1. Unpack the ribbon cassette and turn the knob in the direction shown to take up any slack.
Knob
2. Open the front cover of the printer, using the tabs on each side of the cover.
Tab
3. Remove the old ribbon, if there is one.
4. Insert the new ribbon cassette as shown.
3-10 Setup Rev. E