If you’re using an expression, you would need to use something along the lines of {{ $json.fields["First Name"] }} in value 1, so your If statement knows how to find and use that value. If you’re looking for only people named Frank, you also don’t need an expression in the second value of the ‘if’ statement - you can instead use the ‘fixed’ option and just type Frank.
You can read more about expressions here, which might help give you a better overview!