The experiment-wide compensation will be used for gating in the Gating Editor. You can find more about the experiment-wide compensation in this article here.
To change the compensation, click on the edit pen under the Active Compensation in the Gating Editor. Note that you must do this prior to drawing gates if you want your gates drawn on the new compensation you selected, or your previous gates will be hidden after you change your compensation.
If your files are not compensated and you need to create a compensation matrix, click on the Compensation tab on the right side of the experiment level navigation bar.