ID_Number is declared as Integer or Number?

A number

Just make sure your 'where' returns the item you want

Right, so is the 'Where' field where I get the data from?

The "Where" is set up correctly. You're saying that the item you want to update has an ID that matches your workflow variable ID. The parts after that are the fields you want to update. What you have set up right now is that you want the item where DeviceID == ID_Number and then you're going to be setting DeviceID == ID_Number which should already match. Does that make sense?

Let's say your ID_Number is 5. So you're looking for the item where DeviceID == 5. So now we know DeviceID is 5. Now, you're telling it you want to set the DeviceID of that to ID_Number, both of which are already 5. That's why nothing is changing.

Thanks. I think I'm getting it.

The Device:ID is the column which contains the number I need to query and then return the result to DeviceID. So I thought the Where should be Device:ID and the Field should be set to Device ID?

This is how I've set it up again and I put a Stop Worflow after to see if it works but I'm getting an error and nothing's updating...

So basically, you want to "copy" the Device:ID column into the DeviceID column, is that correct?

yes

Does this run as a list workflow on the item? If so, I would use the "Set Field" action. This way, you're updating the item you're already on and you can set the field DeviceID to the value of Device:ID

Hi. I don't quite understand the question, but the workflow is running on the list and I'm trying to update the DeviceID field with the Device:ID info? I'll look into the Set Field condition.

I've set up another question which might clarify some points: https://community.nintex.com/thread/16657-updating-a-field-uisng-update-item-or-set-value-action