Rekordbox does not "warp" tracks. It allows you to adjust the beat grid so that certain features and elements can work in a quantized manner.
If you have a track with unstable tempo, then you can try analyzing with Dynamic Mode, although this is not always successful. Your next option is to spend some time adjusting the beat grid throughout the track. It will be tedious, but should be possible with some work. However, this will not make the track play to a constant tempo... only adjust the quantization to match the track.
If you want to make the track play at a stable tempo, then your best option is to edit the track with software like Ableton Live. With Ableton Live, you can warp the track and then create a new audio file which has a perfectly stable tempo. Then when you import that new file into Rekordbox you can use Normal Analysis mode and it should be much easier to set the beat grid since now the track will have a constant tempo with no fluctuations.