How to add a particular rewrite rule for URL

I am trying to add a rewrite rule so my URLs change from:

mydomain.com/column/some-post-name

to

mydomain.com/opinion/some-post-name

“Column” is a custom post-type in which these particular posts reside (if that matters at all).

I’ve tried adding the rewrite rule:

RewriteRule ^column/(.*)$ opinion/$1 [L]

in my .htaccess file but nothing happens. I’ve looked at adding something to the the functions.php file for rewrites but can’t figure it out. Can someone let me know what I need to do to get this to work. It would be greatly appreciated. Thanks.