When writing conditions for Additional Content in an Output Preset, the condition should be written as the inside of an IF statement
For example, a condition in JavaScript may be
if(A==B){}
So the condition inside of the Condition field in the OMR would be
A==B
For a more concrete example, the condition for first page would look like this
page.nr == 1
For more on the variables available see here: PlanetPress Connect 2018.1 User Guide
You can make use of any of these to help you build the condition you need.