How to parse a variable to event timestamp

[spartan_07]

I have a log : 
Sample : 

{
    "ts": "2025-04-26T01:45:26.126095Z",
    "adminName": "",
    "adminEmail": "",
    "adminId": "",
    "networkName": "Delhi",
    "networkId": "",
    "networkUrl": "",
    "ssidName": null,
    "ssidNumber": null,
    "page": "Overview",
    "label": "",
    "oldValue": "",
    "newValue": "",
    "client": {
        "id": ,
        "type": 
    }

I want to use the ts variable and put it in metadata.event_timestamp variable . 

How can I parse it? 
Below is a sample parser : 

filter {
        json {
            source => "message"
            array_function => "split_columns"
            on_error => "not_json_format"
        }

        mutate {
            replace => {
                "src_present" => "false"
                "event1.idm.read_only_udm.metadata.vendor_name" => "Meraki"
                "event1.idm.read_only_udm.metadata.product_name" => "Dashboard"
                "event1.idm.read_only_udm.metadata.event_type" => "GENERIC_EVENT"
            }
        }
 
   mutate {
      merge => { "@output" => "event1" }
    }         
}

Can anyone help?