This is how I currently resize sleeves for .21 nitro engines. This is a very inexpensive and easy way to do it but be careful not to overdo it.
The original video where I got this method from: https://youtu.be/WAizS7iXaFM
The tool I used: https://www.amazon.com/dp/B07GTC8VW4/ref=redir_mobile_desktop/135-0179404-1751016?_encoding=UTF8&ref_=sspa_mw_detail_0&th=1