This Ableton Live walkthrough from the Learn Live series shows how to find and reshape Song Tempo automation in Arrangement View. It starts with the setup: pressing A for Automation Mode, then using the Master track's device choosers to select Mixer and Song Tempo, where you can also adjust the visible tempo range to match your project.
Once you can see the automation lane, the real work begins. Automation recorded from scene tempo changes often looks angular, jumping sharply from one BPM to another, which translates into jarring tempo jumps in playback.
The fix is to clear those points and draw new ones that ramp gradually from one tempo to the next instead of snapping instantly. For precise tweaks, holding Shift while dragging a point nudges the tempo by a single BPM, while dragging without Shift moves it in larger increments, giving you control over both the shape and precision of the transition.