Easiest — paste the JSON:

1. Open reddit.com/subreddits/mine.json while logged in to Reddit
2. Select all (Ctrl+A / ⌘A) and copy
3. Paste below and hit Import

Or just type them:

Comma-separated list: sysadmin, PowerShell, homelab

Desktop: bookmarklet method

1. Drag this to your bookmarks bar: 📋 Grab My Subs
2. Go to old.reddit.com (logged in), click the bookmarklet
3. Copy the popup text, paste below