My brother in law gave this machine for me, it was taken out from his nandos shop due to lack of coffee sales. (who can make coffee in nandos chicken shop... )

Its been sitting in his garage for more than 2 years now, it still has water inside (can see from the gauge), I am getting a flojet pump for water supply. How do I flush this and descale the machine?

I prefer to do it myself rather than to call a technician not because I am tight but I love this thing and curious of the mechanism.

Thanks in advance. I can provide pictures, etc please direct me which parts, I don't want to jam the forum with lots of pics.