Water damage under shower.

Hi all! My husband and I just purchased a 2019 Forest River Salem 32 rlds. I was doing dishes and heard a noise.. ran to the bathroom and water was coming from under the shower. Turned everything off and opened the little panel to find my WORST nightmare. Water damage. There’s a hole cut under the subfloor that’s under the shower that apparently has been collecting water from longgggg before it was ours. I don’t even know where to begin with replacing this. Any suggestions or help would be appreciated. This is our first RV and we’re only 2 weeks in.

Also to add... I checked all closets, cabinets, floors around the area and the subfloor does not look to be damaged at all in those areas. Just the area that was cut under the shower.