https://developers.weixin.qq.com/miniprogram/dev/api/file/wx.saveFileToDisk.html

const res = await api.xxxx({
})
const { data } = res
const fsm = wx.getFileSystemManager()
const filePath = wx.env.USER_DATA_PATH + `/xxx_2020_11_11.xlsx`

fsm.writeFile({
  filePath,
  data,
  encoding: 'binary',
  success: () => {
    wx.saveFileToDisk({
      filePath: filePath,
      success: () => {
        
      },
      fail: () => {
        
      }
    })
  }
})