How to make value in tooltip c3 into single value

Question

enter image description here

Hello everyone! I need to know how to make value of tooltip into single value inseat of 2 (date, value)

I would appreciate if anyone can help me

    c3.generate({
      bindto: `#${id}`,
      data: {
        ...this.dataObject,
        columns: data,
      },
      tooltip: this.tooltip,
    });
  }```