Samples trig / Tracks trig

Hi everybody,
Sorry for my newbie’s question, but I don’t find the answer.

I use the OT to launch differents samples. Each sample are on one track :
Sample 1 on T1, sample 2 on T2, etc…

To launch a sample, I press the “sample/MIDI trig”. If I want to stop it, I hold the T1 button and I press “stop”. It’s not very easy on live condition.

I saw on video it’s possible to affect samples on “track trigs”. If I press the button A for example, I launch the sample. If I re-press this button, I stop the sample.
But I don’t know how to affect a sample to a “track trigs” button.

I think I made wrong something, or I didn’t activate a preset.

Can you help me ? Thanks in advance !

Alex.