You can adjust the volume over time of your script or audio layers with volume keyframes:

1. If the Timeline is hidden, click Show timeline in the lower left corner. Click and drag the edge of the Timeline upwards to expand it.
2. Find the clip or audio layer that you want to apply a volume keyframe to, right-click the point where you want to add the keyframe, and select Add volume keyframe. Alternately you can hold Option (macOS) or Alt (Windows) and left-click the point where you want to add the keyframe. You will need to add at least two keyframes to increase or decrease the volume over time.
3. You can then click and drag the keyframe in the Timeline to adjust the volume of your audio and the keyframe's position.