Fanbelt on Corsa 97/98 1.2 Merit?

Hi,
Does anyone know how to replace the fanbelt on a 1.2L 1997 R reg Vauxhall Corsa B shape? I've had a look at it and I can't seem to find the adjustable bolt.

I had to take the cover off the air filter to be able to get to the fanbelt in the 1st place, but now im stuck on how to adjust it so i can replace the fan belt.