Merge two Laravel collections elements and replace

I have this laravel collection called $box_items.

Collection {#320 ▼
  #items: array:3 [▼
    0 => array:6 [▼
      "img_alt" => "<span>Original</span> gifts"
      "class" => "personalised-gifts"
      "elements" => array:2 [▼
        0 => array:2 [▼
          "id" => 2638
          "type" => "ARTICLE"
        ]
        1 => array:2 [▼
          "id" => 2100
          "type" => "ARTICLE"
        ]
      ]
    ]
    1 => array:5 [▼
      "img_alt" => "<span>Love</span> gifts"
      "class" => "love-gifts"
      "elements" => array:3 [▼
        0 => array:2 [▼
          "id" => 1072
          "type" => "CATEGORY"
        ]
        1 => array:2 [▼
          "id" => 6186
          "type" => "ARTICLE"
        ]
        2 => array:2 [▼
          "id" => 1028
          "type" => "CATEGORY"
        ]
      ]
    ]

On the other hand, I have another collection called $elements, this $elements collection have extra information about the 'element' field in the $box_items collection.

This is my $elements collection:

array:5 [▼
   0 => {#313 ▼
      +"type": "ARTICLE"
      +"name": "Ceramic Mug"
      +"resource_id": "2638"
      +"seo": {#314 ▶}
  }

  1 => {#323 ▼
    +"type": "CATEGORY"
    +"name": "Personalised Blankets"
    +"category": {#325 ▼
      +"id": 1072
      +"gallery_id": null
      +"final": true
    }
    +"seo": {#326 ▶}
  }

  2 => {#327 ▼
      +"type": "ARTICLE"
      +"name": "Circle Cushion"
      +"resource_id": "2100"
      +"seo": {#328 ▶}
  }

  3 => {#329 ▼
      +"type": "ARTICLE"
      +"name": "Book"
      +"resource_id": "6186"
      +"seo": {#330 ▶}
  }

  4 => {#341 ▼
    +"type": "CATEGORY"
    +"name": "Gifts for men"
    +"category": {#342 ▼
      +"id": 1028
      +"gallery_id": null
      +"final": false
    }
    +"seo": {#343 ▶}
  }

]

I want replace the $elements CATEGORIES and ARTICLES by the $box_items elements field.

I want this final result:

Collection {#320 ▼
  #items: array:3 [▼
    0 => array:6 [▼
      "img_alt" => "<span>Original</span> gifts"
      "class" => "personalised-gifts"
      "elements" => array:2 [▼
        0 => {#313 ▼
            +"type": "ARTICLE"
            +"name": "Ceramic Mug"
            +"resource_id": "2638"
            +"seo": {#314 ▶}
        }
        2 => {#327 ▼
            +"type": "ARTICLE"
            +"name": "Circle Cushion"
            +"resource_id": "2100"
            +"seo": {#328 ▶}
        }
      ]
    ]
    1 => array:5 [▼
      "img_alt" => "<span>Love</span> gifts"
      "class" => "love-gifts"
      "elements" => array:3 [▼
         0 => {#323 ▼
          +"type": "CATEGORY"
          +"name": "Personalised Blankets"
          +"category": {#325 ▼
            +"id": 1072
            +"gallery_id": null
            +"final": true
          }
          +"seo": {#326 ▶}
        }
        1 => {#329 ▼
            +"type": "ARTICLE"
            +"name": "Book"
            +"resource_id": "6186"
            +"seo": {#330 ▶}
        }
        2 => {#341 ▼
          +"type": "CATEGORY"
          +"name": "Gifts for men"
          +"category": {#342 ▼
            +"id": 1028
            +"gallery_id": null
            +"final": false
          }
          +"seo": {#343 ▶}
        }
      ]
    ]

via Chebli Mohamed