looks like your axolotl has a fungal infection, there are numerous ways to treat the infection..
add 3.5g/l non-iodised salt to the tank water, once treated keep a level of 2g/l to prevent recurrence.
use 100% holtfreters solution to the tank water, once treated keep a level of 50% to prevent recurrence.
use methylene blue baths, half fish dose 10-15 mins daily.
use acriflavine baths, half fish dose 10-15 mins daily.
use mix methylene blue and acriflavine baths, half fish dose 10-15 mins daily.
use black tea baths, 1 bag (or equal volume) per ten litre 10-15 mins daily.
use salt baths, <15g/l (no more than 15 grams per litre) non-iodised salt 10-15 mins daily, please note salt baths are not always advised unless nothing else works as they can be quite stressful and will remove fluid from the axolotl.
there are probably more ie.. almond/catappa leaves etc.. but these are a few options for you.