you can change the start velocity on the keyboard by pressing "C" or "V".
How do I change velocity in Ableton?
To change the velocity of notes without the Velocity Editor open, click any selected note and drag vertically while pressing the ALT (PC) / CMD (Mac) modifier. While pressing the CTRL (PC) / CMD (Mac) key, vertical movements in Draw Mode correspond to velocity changes.
How do I reset my velocity?
If you mean reset the note velocity, hold Alt+Shift while you left click and drag from left to right over the velocity sliders. You don't need to have any notes selected. They will snap to the default level as the cursor passes over them.
How do I reset my MIDI velocity?
If you mean the midi velocity curve for Controllers, that can be found by simply clicking the reset button on the dialog for the velocity curve. Its on the midi settings tab.