DDJ-RX Doesn't have "Tempo reset"

 So I watched a video on youtube where someone showed how to go from a BPM to another BPM by clicking a button called "tempo reset" so he played a track on 128 bpm and went to 98 bpm by just clicking on the "tempo reset" button. Why I want this function is because I want to adjust the bpm in a certain part and in a certain time. For example, I play a drop and after 4 bars I want to go down in BPM and do a live mashup between 2 tracks. Why doesnt DDJ-RX have this function when most of the separate mixers have.