- Re-import your LIVE database on your TEST SITE.
- Go through whatever motions are required to add the fields for your plugins:
- With some plugins, it's just a matter of "Go to Admin > some-page and the plugin will auto update"
- With some plugins you have to run an external SQL script
- etc.

Your database is now updated.

While you're doing the second step, you should take good notes because you'll have to do the same operations when you go live.