One approach...
On the time line, SPLIT the video where you want the dip to occur.
In the clip that is to be faded, click on FX (left-bottom corner).
Click the green + sign in the upper left hand corner.
Click the TRANSPARENCY effect.
Click the chevron to the right of Select Preset and click FADE OUT.
In the effects box move the scrubber (red line) to the far right.
Click the smaller green + sign in the middle of the toolbar to create a keyframe.
You should now see a line sloping from top left to bottom right.
Click on that line near the end of the clip and drag it upwards to the top. This result should be something like this...
Close the effects box and run the time line to see the result. Click FX to modify it.
If the "Transparency" line isn't shown, as above, click the blue icon that to the left of the keyframe display
To delete a keyframe, right-click it and DELETE.
