Unfortunately there is no default way to resize columns in Kanban boards. We do have an improvement request for that under https://jira.atlassian.com/browse/GHS-9236, you can add yourself as a Watcher to get notified on that along the time.
Also, a possible workaround for this would be creating a bookmark in your browser with the following bookmarklet as text:
This sets the width of the left pane to 500px when you run the bookmarklet.
To expand on Jose's answer here's a longer bookmarklet that's a bit more convenient to use.
It keeps the standard size as the minSize and you can set the maxSize to however wide you'd like and then it steps between them using incrementBy.
Hey admins! I’m Dave, Principal Product Manager here at Atlassian working on our cloud platform and security products. Cloud security is a moving target. As you adopt more products, employees consta...
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