To update ServiceDesk_Asset_ID for all the devices in one go we need to use Attribute Editor.
We need to do a Search for all the devices
Click on Locator Tab -> Expand "Devices" -> Double Click "All Devices"
Ensure all landscapes are included in Search In and click on "OK"
You will see all the devices
Now under "Contents" panel select all device
You can press "Ctrl + A"
Right click on any device from the selected devices, Select "Utilities" -> "AttributeEditor"
Click on "Add" link side to "User Defined"
Enter "ServiceDesk_Asset_ID" under right side filter then the attribute is filtered, click on "Ok"
Now the Attribute is displayed, click on Right Arrow to Modify the contents
Uncheck "No Change" box
Select all the contents
Click on Delete to blank the contents and click "OK"
Now the values will go blank for all the selected devices as shown in below screenshot, click "Close" button
Now try to generate Service Desk ticket and check.
NOTE: Open a case with CA Support if issue is still persists.