I take it you mean 1 octave lower than expected? Or did you mean 1 semitone lower?
Some keyboards have a button, or sometimes a pair of buttons, that let you shift the entire keyboard up or down by 1 or more octaves.
Some keyboards have a similar button, or pair of buttons, for transposing the entire keyboard up or down by 1 or more semitones.
Other keyboards have settings for these octave-shift and transpose features, but you need to do some "menu diving" to find the settings.
See page 21 of the Owner's Manual for information on how to enable/disable the Transpose feature, as well as how to set its value. It looks like you can transpose the keyboard up or down by a maximum of 24 semitones (2 octaves).
Thank You for your reply. Actually it is one semitone lower. I'have one button here as key transpose. when i press that it shifts entire keyboard one octave down. I'll try reading the manual as you mentioned. Once again thank You for your reply