In office/excel script, how to change the name of the first series?

Question

I am plotting the data as follows

const chart1 = sheet.addChart(ExcelScript.ChartType.xyscatterLines, r1);

Then, I added another series

let firstSeries = chart1.addChartSeries(); 
firstSeries.setName("Force")

Here, I can set the series name as "Force".

How can I change the name of the initial one (range object r1) to "Torque"?