how can I descale my steam generar iron model 42238 ?

I think you have a Morphy Richards steam generator iron, model 42238.

The manual is here:

http://www.morphyrichards.co.uk/Pdf/IB42238.pdf

You DID check that, didn't you?

It only says to replace the anti scale filter ASAP and how to clean the sole plate.

You could always ask Morphy Richards for their advice.

XXX
February 2016