The averaging plugin lets you compute averages based on events.

You can select from any of the existing event groups, or use your current event selection.

Use the Parameters tab to input your desired settings and hit the COMPUTE button. Prestimulus, poststimulus, and baseline min/max are all relative to the events. Drop Rejected will discard data points with artifacts”

You can control which channels to display using the Channel Selection plugin, which lets you select from presets or choose your own selection.

Computed averages will be displayed in the Data Manager, where you can switch between them.