By default, you can find Replace Edit in the Fast Menu Tool Palette (the Fast Menu that, by default, is between the Splice In and Overwrite buttons as well as in the Timeline Toolbar), and in the Command Palette (Tools menu | Command Palette | Edit tab).
I often call Replace Edit the mysterious blue arrow, because so many don't know what it does and avoid using it. This is too bad because Replace Edit is a very useful tool that allows you to quickly replace existing segments (shots) in your Sequence as well as to sync a specific frame of video to a specific frame of audio (or vice versa).
Since I call it the mysterious blue arrow, which sounds like the name of a cartoon super hero, let me first explain its two super powers, which are as follows:
You don't have to Mark In or Out in either the Source Window or the Record Window when you use it. Replace Edit knows how much to edit into the Sequence based on the duration of the segment that's already in the Sequence...