my house was built in 1890,the main bathroom has a concrete floor, but due to the toilet leaking, the shower water hiting the floor, the wall connected to the floor is rotted, the wooden floor under the concrete that connects to the wall is rotted, how do I fix this
As mike said, a lot more info is needed. Can you get under the floor easily? If yes, then sistering the old joists may work depending how bad they are. In any case you will have to replace some or all of the floor.
Also the wall repair will depend mostly on the wall construction and extent of the damage. If you have mould, then the problem could get bigger!