Perform an intelligent cleaning (all rooms) - it also scans and recognises new rooms. Another option is to place the irobot in the new room and press the home button to return to the station. It could then recognise the new room.
Or a completely new scan...

Thanks for the tips.

select "My home" there is "Map1" and further down "+ Add new room" then continue and let the cleaning robot measure the room. is actually self-explanatory.
there is also help and instructions in Support