Not a problem my friend the Titles you should buy are The Manual of Koi Health ISBN 9781842862377 by Keith Holmes and Tony Pitham .
Another good one for your level of entry to buy would be as follows Koi Health and Disease "Begginer to advanced Life Saving Technology No ISBN By Erik L Johson DVM , note he also did a 2006 reloaded version of this and there is also a brand new version of ths Called Koi Health and Disease 2 .
These books will put you in good stead for the future you will b able to secure a copy over the internet from Amazon Books under koi health books .
If you think the wound is turning bad please give me a shout but I dont think you'll need to my friend .
Remember what I said about netting technique come gently up behind the koi and lead it to the surface with a 22" pancake net, practice it Alp do you have a sock net my friend.....if not buy one they are very useful one for scooping the koi from the pancake net , then holding the bottom of the net and the handle you can move a koi from A to B then simply after putting the end of the net into either a bowl or plastic bag gently deposit the koi with no stress to it or you
Dave