CodaKid provides you with a template of the textures just in case something were to go wrong with them. To find your mobs texture you Will need to go into src/main/resources -> assests -> TEMPLATES -> TEXTURES -> MOBS
Here is a picture with the correct folders open.
From there locate your mobs texture and then copy it, then go back to the folder where your damaged texture was in and delete the damaged texture. After you have deleted the broken texture, paste the new texture into the folder and then make sure to change the name of the texture to the name that the old texture had. To rename it left click the file once and then then right click it. Select properties. A window will appears, select the button circled below:
A new window will appear from there.
Left click the file that you are going to rename then right click it and select rename. Type in the name you want to give it and then close both of the windows that opened.