how to convert geo month to jalali date in export dhxgantt

I have Using From Dhxgantt And exporting api Too,
I am Iranian And Convert Date To Jalali , But When I export to Pdf Or Png Or others in Export Month Is Gregorian , Please Help me!! :frowning: :frowning: :frowning: :frowning: :frowning: :frowning: :frowning: :frowning: :frowning: :frowning: :frowning:
please help me