How to include apt in ubuntu 18.04 image – device

How can i add the apt to my Ubuntu 18.04 image below is my json file:

    {
      "type": "model",
      "authority-id": "9J3P2BX7g8sU6A1xWGDQhC",
      "brand-id": "9J3P2BX7g8sU6A1xWGDQhC",
      "series": "16",
      "model": "ubuntu-core-18-pi-arm64",
      "display-name":"Ubuntu Core 18",
      "architecture": "amd64",
      "base": "core18",
      "gadget": "pc=18",
      "kernel": "pc-kernel=18",
      "required-snaps": ["core", "usbmode-switch","easy-openvpn","fast"],
      "timestamp": "2022-02-02T10:43:16+00:00"
    }