Schema Markup campo data nel formato ISO 8601 (YYYY-MM-DDT00:00:00Z)

I entered the following schema but google reports "startDate" not compliant with ISO 8601 format (YYYY-MM-DDT00:00:00Z) how can I convert the field [Field 124] from 4 april 2025 to ISO 8601 date format?

{
"@context": "https://schema.org",
"@type": "Event",
"name": "[Page Title]",
"description": "[Intro Text]",
"image": "[Page Image]",
"startDate": "[Field 124]",
"endDate": "[Field 124]",
"location": "[Field 125]",
"performer": {
"@type": "Person",
"name": "[Page Title]"
}
}