OK, i think i understand what you want to. At First you must identify the Dataset you want to change. I take the USR_OH_Idnr, but you can also use every SELECT you wish to Identify your Dataset. To Modify the Checkbox you can use nearly the same as in the select query.
UPDATE USR SET USR_PwChange=TO_DATE('01.01.60','DD.MM.RR') WHERE USR_OH_Idnr='1xxxxxx'
If you execute the query, the box will be set. If you need to unset it, set it to a date in the future. NOTE it is not enoufh to set the day in past. It must be the query above to set the checkbox for the sepcified user.
Best Regards