How to convert string in textview to HTML in Swift?

Question

I have a UITextView. I want to post the string written in this textview to the API in accordance with the HTML structure.

For example, I want the text user bolded in the Textview to be suitable for HTML.

I am using the following structure to convert HTML data from API to AttributedString and it works. But I couldn't find a solution for the opposite situation. Could you help ?

extension String {    
    func htmlAttributed() -> NSAttributedString? {
        let htmlCSSString = "<style>" +
        "html *" +
        "{" +
        "font-size: 12px ;" +
        "font-family: AvenirNext-MediumItalic;" +
        "color: #6098A1 ;" +
        "}</style> \(self)"
        guard let data = htmlCSSString.data(using: .utf8) else { return nil }
        do {
            return try NSAttributedString(data: data, options: [.documentType: NSAttributedString.DocumentType.html, .characterEncoding:String.Encoding.utf8.rawValue,], documentAttributes: nil)
        } catch {
            print(error.localizedDescription)
            return nil
        }
    }
}