blazer transfer case keeps slipping into neutral

My transfer case keeps slipping into neutral. When my friend pulls me it starts to work aging. It slips out when I stop. I was playing in a water puddle and abut 15 MIN later I can’t get it out of 4low now it will only go in to 2hi and 4hi. It will shift into neutral and 4low but it won’t be in neutral and 4low. When I shift into neutral it will stay in 4 hi and the same for 4low. If any one know's what I need to do please let me know. Thank you. year 1985