It depends on how we interpret the question.
Using the generally accepted lapse rate of 30 hPa per 1000 feet, the 10 hPa difference between 1013 and 1023 equates to about 333 feet. The author of your question appears to have rounded this off to 300 feet, so let’s use that figure.
With 1013 set the altimeter will indicate altitude above the 1013 hPa pressure level. This is above the 1023 hPa pressure level, so with 1013 set the indicated altitude will be less than the actual altitude.
If you keep 1013 set and level off at 4000 feet indicated your actual altitude will be about 4300 feet.
If you keep 1013 set and level off at an actual altitude of 4000 feet your indicated altitude will be about 3700 feet.
If you select 1023 and level off at 4000 feet indicated your actual altitude will be about 4000 feet.