iOS Swift how to convert time to ISO format

Have below extensions

extension Date {
    struct Formatter {
        static let iso8601: DateFormatter = {
            let formatter = DateFormatter()
            formatter.calendar = Calendar(identifier: .iso8601)
            formatter.locale = Locale(identifier: "en_US_POSIX")
            formatter.timeZone = TimeZone(secondsFromGMT: 0)
            formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSXXXXX"
            return formatter
        }()
    }
   
    var iso8601: String {
        let formatter = Formatter.iso8601
        formatter.timeZone = TimeZone(abbreviation: "UTC")
        return formatter.string(from: self)
    }
   
    var iso8601IST: String {
        let formatter = Formatter.iso8601
        formatter.timeZone = TimeZone(abbreviation: "IST")
        return formatter.string(from: self)
    }
   
}


extension String {
    var dateFromISO8601: Date? {
        var data = self
        if self.range(of: ".") == nil {
            // Case where the string doesn't contain the optional milliseconds
            data = data.replacingOccurrences(of: "Z", with: ".000000Z")
        }
        return Date.Formatter.iso8601.date(from: data)
    }
}