I know what that is. That may be an infection. He/She may not live so do the following.

1 If you have other salamanders divide that one away from the others to prevent infection to spread.

2 If it doesn't eat try to feed it.

3 Keep tat salamander away from light to make sure if it is what I think it is it won't aggravate the pain.

4 If that opens up.... This is the tough part... You must put it out of it's misery.