Edit in JSFiddle

let chart = c3.generate({
    bindto: '#chart',
    data: {
      columns: [ ['data1'], ['data2'] ],
    }
});

const load = document.getElementById('load')
const unLoad = document.getElementById('unload')

load.querySelector('button').addEventListener('click', () => {
	displayButtons()
  chart.load({
    columns: [
      ['data1', 300, 100, 250, 150, 300, 150 ],
      ['data2', 100, 200, 150, 50, 100, 250 ]
    ]
  });
})

unload.querySelector('button').addEventListener('click', () => {
	chart.unload('data1');
})

function displayButtons() {
	load.className = 'hidden'
  unload.className = ''
}
<p id="load">Click here to Load Data → <button>Load!</button></p>
<p id="unload" class="hidden">Click here to Unload Data1 →  <button>Unload data1</button></p>
<div id="chart"></div>
.hidden { display: none }