That's easy.
'sudo' is the keyword you start with to say "I have permission." ... you just must provide the password for the machine as well.
--
For this error
ln: /usr/local/Cellar/libidn/1.23/lib/libidn.11.dylib
you'll need to adjust the version number.
do:
ls -la /usr/local/Cellar/libidn
And it will show you what version you have. Use the same code from before, now just, modify the version of that target. I had like, 1.11 for example, not 1.23.