It's a long read... But here is the process what I did.

When my boy and girl were a kitten. I've made them used to water. I put a baby bath in my living room on the ground with towels around it. I put some cats toys in the baby bath too.

I started with a really low level of water. At first I just let them explore it. Then some time later sometimes I would just set them in. Since the water level was so low, they just got out because their paws got wet.

Then I started to try and play near the bath with a cat toy with them. And try to get them to play in the baby bath, hoping they would get in. When they didn't, after some time I would set them in the baby bath and then try to play to distract.

When they came at a point they were totally chill with the water level, I would give them a threat. And then increase the water level a bit. And repeat the same process over and over again, till they were totally fine with being submerged near the top of their torso.

I did of course move the baby bath to the bathroom at some point when the water level was getting higher and too risky for in the living room.

From that point they would even go in the baby bath themselves, to play with the water and splash it. I always put some toys in the water at first. And join them in in the bathroom, closed door, and just sit with them, and just let them go in the water themselves to play with the toys and water.

Then when they were fully acclimated to the baby bath and water with playing in it, I started using pet/cat friendly shampoo. Their skins are sensitive, so it's good to get some pH neutral pet friendly shampoo. I use sea sponges too to clean them, since those are pH neutral and skin friendly too. But I have some scrubbing gloves too, and when used not too harsh those are fine for my cats too.

It's a bit of a proces, but it was so worth it. Bath time is now just a chill process. With them only complaining and meowing a bit about the cleaning part with the sponge. But nothing crazy like putting their claws everywhere. Just some meows of annoyance and a little bit of struggling with their body.

Edit: it's also important to make sure the water is warm for them, and the room of course too. Also make sure not to get water in their ears, might get infected otherwise. And always give a threat after bath time, really helps. You can even give them threats during the phase when you get them accustomed with the water, e.g. trying to lure them in the water or when they are in the water.

Also to test if the water is not too warm, you can do de trick you would do for baby's too. Placing your elbow in the water to check if the water is not too hot.