Rubber wearing is much progressed at "shoulder area" of tread.
Underinflation will lead to excessive tread shoulder wear. It will also lead to high tire deflection and subsequent heat build-up which may result in tire damage.
If the tire wear limit has been or soon will be reached, remove the tire.
If the wear limit has not been reached, check the pressure and adjust it to the recommended value. If shoulder wear is more pronounced on one side, this type of wear could result from axle flexing. Tire can be kept in service until normal wear removal criteria is reached.