Change font settings

1. Select the shape by name you want to modify. See here to find shape names.

2. Under settings, insert desire font under chartFont and font size under chartFontSize

Reference:

Download: input.zip | output.pptx

---

{
  "presentation": {
    "template": "template.pptx",
    "export_version": "Pptx2010",
    "slides": [
      {
        "type": "slide",
        "slide_index": 0,
        "shapes": [
          {
            "name": "Chart 1",
            "settings": {
              "chartFont": "Trebuchet MS",
              "chartFontSize": 30
            }
          }
        ]
      }
    ]
  }
}