You can’t reset millis() but you can offset it.
Example:
var off = 0;
function setup() {
createCanvas(400, 400)
}
function draw() {
background(220)
textSize(48)
textAlign(CENTER, CENTER)
text(int((millis()-off)/100), width/2, height/2)
}
function mouseClicked()
{
off = millis();
}
:)