Simply Koi and More Koi

Hi all am a newbie, wanted to know best thing for Costia, lost a koi last nite, before it died I scraped it and found Costia also sum raised scales with red marks, thnxs

The raised scales are not a parasite syptom. But ofc when a fish is attacked by parasite its immune system becomes more vulnerable to other infections. The red marks could easily be from the fish flashing (/rubbing) itself on different areas.

But first things first, we have to know how well you water is. Do you have no ammonia/no2/no3? What is your ph value, is it stable? What is the temperature of your pond?
If everything is okay then you can treat.
ICC Duncan style could do it after using salt or using FMG. Preferably not a premix FMG but it could still do the job.

We do need more details though. Also pictures could be very useful.