How to change the format of X-Axis/Y-Axis values?

The format of X-Axis/Y-Axis values can’t be changed.
such as, percentage or million.

That’s right, you can’t. Workaround is to change the question to return the values in a better format, though that won’t always work. I’ve not checked, but I’d be surprised if this isn’t on the list of future enhancements.

Hope it will be improved soon.