It's a rebadged boiler, not sure if Ideal or Glowworm...the case shape looks Glowworm.....but that's not important right now.
Fit the temporary filling link.
Pull the black lever on the right valve towards you to open it. If stuck take its handle off using a crosshead screwdriver, then use an adjustable spanner to turn the shaft anti-clockwise 1/4 turn when viewed from the right.
Open the other black handled valve to fill the system, close it when up to pressure.
Close the original valve before removing the link and re-attaching its lever.
Job done.