Ok... I never deal with those issues (rarely a need to have special chars in DNS here) but I presume there are some online pages
where you can do the conversion. I found this one: https://www.punycoder.com/
The only risk with running some tool like that without first examining what it exactly does is that, when you are using it on a
domain name you would like to register, the website quickly registers it and takes the name as hostage to have you pay.
It has happened before with sites that offer you to check if a domain name is available and when you just enter some name
there, the answer is that it is already registered but that you can buy it from them....