Update Attribute datatype from String to Array

I have a problem. I want to change the data type of an attribute from String to array.

      "id": "trn:tarb:tradingpartner:uuid:00000464-fa72-49fe-b050-c4bf1cfd8259",
      "partnerNumber": "1098981",
      "partnerName": "AFLO ",
      "currencyCode": "GBP",
      "commercialPartnerStatus": "Inactive",
      "source": {
        "id": "STV0001$$",
        "name": "QS"
      "corpCode": "DR",
      "subCorpCode": "001",
      "targetMarket": "UK"

In the above one, I want to change targetMarket which is in String currently to array as like below without changing its name.

UPDATE default AS d
SET d.targetMarket = ARRAY_APPEND(TO_ARRAY(d.targetMarket),"IN")
WHERE d.targetMarket  IS NOT NULL ;