If there's just one option hitting Space or Enter should do the trick, as the button should be preselected. If there are more than one option you could tab between them by enabling All Controls under System Preferences / Keyboard / Full Keyboard Access.

Then tabbing through the options, a subtle blue glow will highlight the tabbed option. Hitting Space will select it, while hitting Enter will select the default option.

If there's just one option hitting Space or Enter should do the trick, as the button should be preselected. If there are more than one option you could tab between them by enabling All Controls under System Preferences / Keyboard / Full Keyboard Access.

When tabbing through, a subtle blue glow will highlight the tabbed component. Hitting Space will use it, while hitting Enter will use the default option.