Hello Shuqair,
According to SDK Help file for SAP Business One DI API 9.1, OHED table is not exposed through DI API. Therefore I don't think it is possible to add Education Type via DI API. You can check the EducationType Property and EmployeeEducationInfo Object Members subjects for this information.
Let see if any SAP Support member can also verify this information.
Also you can check the below thread to have an idea about the situation
SBO Tables NOT exposed in DI API | SCN
Kind Regards,
Atilla.