There is currently no option to Mass Update the Organizer of an Event.
Alternative solution is create a custom Mass Update that will run a script changing the Organizer.
Here are the steps:
function massUpdate(recType, recId)
var rec = nlapiLoadRecord(recType, recId);
rec.setFieldText('organizer', 'Name of New Organizer');
Note : Name of New Organizer should be the exact name of the Employee seen on an Event Record
2. Save the file as MassUpdate_Event.js
3. Navigate to Customization > Scripting > Scripts > New.
4. On the Script File field, click the "+" symbol and upload the MassUpdate_Event.js file.
5. Click Create Script Record.
6. On the Select 1.0 Script Type, select 'Mass Update.'
7. On the Script page, set the following:
• Name : Mass Reassign Events
• Scripts tab > Function field : massUpdate
6. Click Save and Deploy.
7. Set the following fields:
• Status = Released
• Applies To = Event
8. On the Audience tab, specify the Roles that can access the Mass Update.
9. Click Save.
Performing the Update:
1. Navigate to List > Mass Update > Mass Updates > Custom Updates.
2. Click 'Mass Reassign Events.'
3. Add Criteria to search for the Events that have to be reassigned then click on Preview.
4. Click Perform Update once satisfied with the records.
Once the Mass Update is complete, events will be assigned to the employee specified on your script. Modify the script for each new organizer.
Enhancement 159334 (Mass Update of Event records) is in place.