Question about FM 'SAP_WAPI_GET_DEADLINES'

hello all,

this FM 'SAP_WAPI_GET_DEADLINES' is returning times and date from workitem, my question is that i want change the time and the date and save them in Workitem, and when i call again the FM 'SAP_WAPI_GET_DEADLINES' it schould return the changed time and date, so can anyone show me which FM shall I use to update or to save times and dates in Workitem? i have 3 kind of time and 3 kind of date and all of then should be saved at once,

thank you all