Congratulations! Your Jolida Music Envoy monoblocks incorporate "Easy-bias".
To adjust the bias a small screwdriver is needed. Let the amplifier warm up for 10 to 20 minutes and disconnect all inputs. Next to each output tube (tube type 211 labeled V5 and V6), there is a LED diode (red or green depending on model) and a small adjustment potentiometer. If the LED is not illuminated, turn the potentiometer clockwise until it is (this increases the bias).
During the lifetime of the tube if the LED goes out, it means that there was a "drift of bias". This means that the resistance of the tube has changed slightly as the tube ages. Repeat the biasing procedure until the LED lights. If the LED does not light when the potentiometer is in its fully clockwise position it means the tube cannot obtain bias and must be replaced. Normally both output tubes should be replaced as matched pairs even if one cannot be biased.