How to start counting again when for exceeds a certain value?

I have this for that generates a series. The main problem is that I only have 9 colors.

for (let i = 0; i < dataZCsv.length; i++) {
    let colorNumber = i;
    if (colorNumber > 8) {

    }
    let dataBlok = {
        name: nazvyZCsv[i],
        data: dataZCsv[i],
        visible: jednaStopaTF,
        regression: hodnoty.trendy,
        regressionSettings: {
            type: 'polynomial',
            color: Highcharts.getOptions().colors[i --> colorNumber],
            dashStyle: 'ShortDot',
            name: " ",
            hideInLegend: true
        }
    };
    serie.push(dataBlok);
    serie[0].visible = true;
};

So even if i exceeds 8, it will start writing i greater than 8 to the color: Highcharts.getOptions().colors[i] and this is problem. I have only 9 colors. So I need to do that when it exceeds 8, it starts counting again from 0. But i still need to use it in other variables (name: nazvyZCsv[i], data: dataZCsv[i]), where it must be up to the maximum value (dataZCsv.length).

Ideally, I would make a separate variable for the color number colorNumber, which when it reaches 8 starts again from 0 to end of dataZCsv.length.

Something like:

let colorNumber = i;
if (colorNumber > 8) {
    colorNumber = 0;
    colorNumber++;
}

or:

let colorNumber = i;
if (colorNumber > 8) {
    colorNumber = 0;
    for (let j = 0; j < dataZCsv.length - 9; j++) {
        colorNumber + j;
    }
}

But this not work in for

I've been stuck for several hours and I still don't see a solution. Can you help me, please?