If you mean to ask how to set alpha for the power analysis to your desired value, the box in the Power Analysis outline is editable.
The Full Factorial Design platform does not provide the Design Evaluation outline. In your case, click Make Table, then click the green triangle next to Evaluate Design table script. You will find the Power Analysis outline there.
If you are evaluating several candidate designs, proceed to make the data table for each one and then select DOE > Design Diagnostics > Compare Designs. This analysis platform provides a side-by-side comparison of the candidates, including their power.