"Tempo Smoothing" is the phrase I use when you take an audio track (or tracks) which wasn't recorded to click with a fluctuating tempo. I then tempo map it and ultimately "smooth" the tempo so it has a fixed BPM.
Samplitude doesn't have tempo smoothing implemented but I worked out a way to do it. Warning!! it isn't a one click solution and involves a few steps to achieve this. If you enjoy probing into the inner workings of Samplitude you may enjoy this. But if you're in a hurry this it's a longish video just over 14 minutes so you may find this is not for you. This technique needs Samplitude Pro X3 or Sequoia 14. Useful timestamps are below:
Calculating the initial Tempo 01:34
Tempo Mapping the song 03:14
Showing the Tempo Track envelope 06:46
Splitting the objects at marker positions. 07:22
Freezing the track and enabling musical tempo adjustment 11:19