Err7 is a motor error, which mostly results from a motor disconnection. Here is the cure.
Number one: disconnect power and shut off the water supply to work safely.
Get the washing machine out of the cabinet and place it in such a way as to access the rear part of it.
Undo the 3 Phillips screws holding the small rear plate (not the whole rear panel!)
Peep into the hole and look at the motor, which is located at the bottom. Probably, you will see a disconnected 7-way connector and a 7-way socked lying idly on the motor. This can be considered a happy end!
Connecting it won’t pose any serious trouble: there is simply no room for a mistake. To ensure a firm connection, press on it a little harder several times, so that it won’t come apart again.