You would design the speakers to fit the room, instead of fixing the room.
It’s another way of saying get the appropriate speakers to fit the size of the room, which I agree. Generally, small speakers for small rooms, large speakers for large rooms. However, that doesn’t work out that way all the time as mentioned by few people here. Some speaker designs allow close placement to wall boundaries while some designs require the speakers to be placed out of the room with considerable free space from the rear and side walls. With the former, large speakers may be able to fit smaller rooms with minimal ill-effect to the sound reproduction.
I have mid-sized monitors in a long and narrow room measuring 10.5’ x 20’ x 9’. All my speakers require space from the wall boundaries hence they are selected based on the size to fit the room. I have tried larger speakers in this room and they don’t sound as good as the smaller speaker.