Illness/Sickness: Long Toed Salamander rather Wrinkly

Hello, so yesterday around noon I found my Long toed Salamander curled up and looking very shriveled in the corner of its enclosure. I immediately put it in its water dish thinking it just had not been into its water in the past few days. So for the rest of the day I was checking on it about every 15 minutes or so making sure he was ok. While watching it last night I noticed an indent on its tail like it was rotting or something. After researching today, I believe I have determined it is sick, but then again I have had it for about 4 1/2 years now so it could just be dying sadly It also will not eat whenever offered food. About 2 hours ago I decided after looking at multiple threads quarantining it would be a good idea especially if it's main enclosure could be causing the problem. After over a day of soaking it in the water multiple times, to where its even stayed in the water for over an hour, it's skin still looks rather dry and wrinkles are still visible along with the tail indent. I need help because this little guy has been a rather large part of me growing up and if I can do anything to help him feel better I would gladly do it. Also, I have pictures attached below of him in his current state and his tail. Thank you, and have a wonderful day.

It wouldn't let me upload two pictures at once so here's a picture of its tail too.