Hi Ashleigh,
The "dataset" variables will not work within the same form because technically those values are not updated until the form is submitted.
As a result, if you use {dataset/variable} as a default on the same form in which it is first populated, you would get no result until the next step in the process.
However, what you are trying to accomplish can be done with Functions. Instead of setting the default, set a function that will match the value of your second field to that of the first field.
It looks like you are using Tables/Collections, so I would need a bit more information to provide a working example, but a basic example would be to go under the "Advanced" tab and enter something like this in the Function field:
=Server_Question_1.Client_Steps
The ">" button will give a list of the available values to make sure you get the right ones.