SEO - Duplicate URLs with/without trailing slash

[evcom]

I'm working on SEO and SERPs issues and I came across duplicate URLs.
From what I understand, a specific page should in general not be reachable via multiple URLs. I also learned that using a trailing slash or not is a personal choice and should not have an effect on the ranking. Also, one resource stated, that if a page is reachable (Status Code 200) with and without trailing slash, that this is likely to have no big effect on SERP but it will effect page authority as the link juice is spread over two URLs.

Example:
https://www.mysite.com/forums
vs
https://www.mysite.com/forums/

Situation
For instance, on https://invisioncommunity.com/forums/ can be reached with and without trailing slash, both URLs report Code 200. Canonical tag is https://invisioncommunity.com/forums/
https://invisioncommunity.com/news/ (blog) can only be reached with trailing slash, ../news is redirected to ../news/, canonical tag is set to https://invisioncommunity.com/news/ 
On my site, the blogs main page on https://www.mysite.com/blogs/ is reachable with and without trailing slash and no canonical tag applied...

Question:
Do you think that duplicate URLs are an issue that should be resolved, e.g. at least for the main forums page? I guess it would have to be done via a 301 redirect in .htaccess?
And how can I set a canonical tag to the blogs main page without modifying files? 

Or would you consider the results from an SEO perspective negligible?

[evcom]

I came across this blog article that digs into .htaccess redirects. However, I am afraid I am doing more damage than it would help, so I will probably leave it as it is. 
Goo idea? 🤔