Learn about Weld tool - https://help.sketchup.com/en/sketchup/dividing-splitting-and-exploding-lines-and-faces
Select the two arcs, right click on them and select weld, you can assign a shortcut as long as you have something selected on the model space before going to the preferences. In this case the arc will be converted to a curve because it’s formed by different arcs but if you have arcs or circles that by any reason have been exploded, you can use Curvizard to reconvert them to arcs or circles, the native weld feature just convert lines to curves.
