Hi,
are you talking about Fusion Standalone or Fusion-in-DaVinci?
If you are in DaVinci, you could right-click on your clip on the edit page and choose "Change clip speed".
In Fusion Standalone you can add the node "Miscellaneous -> TimeSpeed".
For a changing starting point of one clip you could open the "Keyframes" panel and either keyframe your effect, or drag the start and end of your single clip.