You can change the speed of the video clip in Wave.video. In order to do it, head over to the step Edit and simply select the speed you want.
By default, the video speed is set to 1. If you select anything smaller than 1, your video will play slower. And vice versa: in order to speed it up, choose a number bigger than 1.
The maximum speed you can set your video to is 2x, which means it will play twice faster as the original clip. The "slowest" speed is 0.25, which means it will play at a quarter of the original speed.