Nested list of maps add or update another nested key

I have a nested list that should follow a rules to update a record or add a record.
I have a keys list which is the path I need to update or add

Entry list

[
      %{
        name: :actor,
        opts: [
          struct: MishkaDeveloperToolsTest.GuardedStruct.NestedConditionalFieldTest.Actor,
          derive: "validate(map, not_empty)",
          hint: "001-1-map",
          validator: {ConditionalFieldValidatorTestValidators, :is_map_data},
          __tag__: "root"
        ]
      },
      %{
        name: :actor,
        opts: [
          derive: "sanitize(tag=strip_tags) validate(url, max_len=160)",
          hint: "001-2-url",
          validator: {ConditionalFieldValidatorTestValidators, :is_string_data},
          __tag__: "root"
        ]
      }
    ]

For example I have a keys list like this ["root", "aa"], and I want to add new record to the list

1. I need to find is there a list that has __tag__: "root::aa" if not add another map to bottom of the list
2. if it can be found, I need add a map inside fields key

When can not find

[
      %{
        name: :actor,
        opts: [
          struct: MishkaDeveloperToolsTest.GuardedStruct.NestedConditionalFieldTest.Actor,
          derive: "validate(map, not_empty)",
          hint: "001-1-map",
          validator: {ConditionalFieldValidatorTestValidators, :is_map_data},
          __tag__: "root"
        ]
      },
      %{
        name: :actor,
        opts: [
          derive: "sanitize(tag=strip_tags) validate(url, max_len=160)",
          hint: "001-2-url",
          validator: {ConditionalFieldValidatorTestValidators, :is_string_data},
          __tag__: "root"
        ]
      },
     // add new map last of the list
     %{
        name: :actor,
        opts: [
          derive: "sanitize(tag=strip_tags) validate(url, max_len=160)",
          hint: "001-2-url",
          validator: {ConditionalFieldValidatorTestValidators, :is_string_data},
          __tag__: "root:aa"
        ]
      }
    ]

When we find it

[
  %{
    name: :actor,
    opts: [
      struct: MishkaDeveloperToolsTest.GuardedStruct.NestedConditionalFieldTest.Actor,
      derive: "validate(map, not_empty)",
      hint: "001-1-map",
      validator: {ConditionalFieldValidatorTestValidators, :is_map_data},
      __tag__: "root"
    ]
  },
  %{
    name: :actor,
    opts: [
      derive: "sanitize(tag=strip_tags) validate(url, max_len=160)",
      hint: "001-2-url",
      validator: {ConditionalFieldValidatorTestValidators, :is_string_data},
      __tag__: "root"
    ]
  },
  %{
    name: :actor,
    opts: [
      derive: "sanitize(tag=strip_tags) validate(url, max_len=160)",
      hint: "001-2-url",
      validator: {ConditionalFieldValidatorTestValidators, :is_string_data},
      __tag__: "root:aa"
    ],
    // add the map inside fields
    fields: [
      %{
        name: :actor,
        opts: [
          derive: "sanitize(tag=strip_tags) validate(url, max_len=160)",
          hint: "001-2-url",
          validator: {ConditionalFieldValidatorTestValidators, :is_string_data},
          __tag__: "root:aa"
        ]
      }
    ]
  }
]

As you see I added it inside the last map and add fields keys.

It should be noted the path keys can have 3 or 4 etc items and my code needs to implement none-limit nested map. for example:

 __tag__: "root:aa::bb::cc::gg"
["root", "aa", "bb", "cc", "gg"]

Thank you very much for your guidance