I'm editing videos of a sport (rowing) where I want to keep the first several seconds and then slow down the motion for several frames and then resume the video at normal speed.

I am using Ultra and so far, after selecting video speed and making the desired adjustment, the entire video changes and not where I selected for the change to start.

Any suggestions, or is this editing feature not available? Or, is there a specific "trick" I need to learn

If not available, is it available in Ultimate?

Thanks