Charts with data from the future

There is an apex chart for electricity prices, which looks like shown below.
I also pasted the yaml code for it.

I need some explanation to be able to show similiar data.

  1. Where do I find the entity “sensor.epex_spot_de_price” from the code below? It does not show up as you can see in the picture below when searching for the entity.
  2. How do I store the attributes (“return entity.attributes.data.map”) in the entity?

The data I have are now json data in a python script. I want to show them in homeassistant.

type: custom:apexcharts-card
header:
  show: true
  title: Electricity Prices
graph_span: 48h
span:
  start: day
now:
  show: true
  label: Now
series:
  - entity: sensor.epex_spot_de_price
    name: Electricity Price
    type: column
    extend_to: end
    data_generator: >
      return entity.attributes.data.map((entry, index) => { return [new
      Date(entry.start_time).getTime(), entry.price_eur_per_mwh]; });