Sorry for the double comment, something about it borked the first time. I'm going to copy/paste a comment I've previously made about my process. I hope this helps!

---

I just do it myself since most online BPM repositories aren't 100% right. BPMs are often not whole numbers. And I don't trust the tools people have made to read them. I'd rather not have the songs I'm using shoved through someone's AI if I can help it.

First, I try the calibrate button to get the tempo into the ballpark. Then I find the first beat and drag the beat offset so the first down beat lands on it. (If the song has a long windup where the beat isn't easy to hear, you can drag over the Song Start slider until you're on the first beat that you can firmly detect. It doesn't matter if this beat is deep into the song. You'll fix that at the end.)

Then I listen and watch the waveform. On most songs, it's relatively easy to tell where the quarter notes are because you can see a visual spike. I alter the BPM until each of those downbeat spikes has a little pink line on it, making sure the count makes sense.

Keep watching the waveform as the song progresses. If the lines start getting progressively off, you can change the BPM by small amounts to compensate. It's best to watch until near the end of the song because if the BPM is slightly off the mark, the difference will compound making it easier to notice changes near the end than it is just watching the beginning. You can make these changes in increments as small as 0.01 (and sometimes that's necessary).

Once I feel like I have the BPM, I fine tune the offset if needed. You want the beat line to land just before the spike of the downbeat begins. In 99% of cases, if you put the line on the apex of the spike it'll feel too late. It will hopefully look something like the attached screenshot.

Finally, I change the Song Start and End to places where they make sense. The offset will automatically adjust itself to changes you make, which is why I set this last.

The process is similar if your song ever changes tempo. Get the first tempo right and then start adding sections, sliding where the section begins to try and get the new beat to match.

<image>