How do I train myself to enjoy a shower again? Or to see a long hot/warm bath as relaxing? instead of triggering past memories.

Breaking down your goal of enjoying a shower or bath into smaller parts can help you to relearn your association without becoming too overwhelmed. Aim to just stand under the shower/sit in the tub for a couple of minutes without the expectation of having a full clean and be mindful and experience the feel of the water on your skin. Work up from this daily. Use breathing exercises to calm anxiety. You can also use any positive associations you have with certain smells and use products with that positive smell. For example if your grandma used lavender and you associate her with comfort. Using these techniques you can recondition yourself to enjoy showering and bathing yet again. Good luck.

You could stop or skip showering for a few days, a week and a half. when you get a shower again you're gonna feel so much relief, almost an spiritual relief. Also it helps to listen to music while showering

One suggestion that I have would be to use the psychological technique of conditioning. If you begin to associate something that you really love with a warm bath, such as reading your favorite book in the bath, it will help you learn to enjoy it.

You have to tell yourself that it is going to be just fine. You have to face your fears and try not to think about your past memories. Slowly the triggers will go.

Set the environment as calm, relaxing and safe. I like to light some candles, dim the lights, light some incense or scented oils, essential oils are great! A few drops in the bath can definitely relax you, and breathe, if it gets too much and you find yourself beginning to panic, hop out of the water again, and once you’re feeling more calm, try again, repeat until it seems normal again :) I try to associate the water with new memories as opposed to old ones. Bring someone with you, a friend or spouse, even a pet sometimes (if they’ll allow you) if you feel comforted not being alone in the water.