How to add rel=nofollow to external links

<a href="https://www.example.com" rel="nofollow">Test</a>

All comment links automatically get a nofollow.

https://codex.www.ads-software.com/Nofollow

I am using a program called SEOpressor and they recommend my using rel=nofollow for my external links for ranking better on Google and improving my SEOpressor score. What is your opinion?

I also have another error on my site at https://www.bestrcboats.com which is “You do not have ALT tag set to your keyword” would you know how to correct this issue in wordpress?

Thanks
Gene