If a change has gone wrong or a site has been damaged, a restore puts things back. What matters is doing it deliberately.
Before restoring
Take a copy of the current broken state first. It sounds odd, but a restore overwrites, and the broken version sometimes contains work you have not replicated - or the evidence of what went wrong.
Restoring
- Open your hosting service and choose Advanced Control.
- Find the backup or restore area.
- Choose the point to restore from - as close before the problem as possible.
- Choose whether you need files, the database, or both.
- Confirm, and wait for it to finish.
Files or database?
- Broken by a plugin, theme or code change: files.
- Content deleted or corrupted: the database.
- Compromised, or you are not sure: both, from a point you are confident predates it.
Restoring only half a pair can leave a site whose code and content disagree, which is its own kind of broken.
Afterwards
Check the site properly - front page, a few inner pages, forms, and the admin area. Then work out what caused it, or you will be doing this again.
Keep your own copies too
Platform backups are a safety net, not a substitute for your own. Anything you could not bear to lose should exist somewhere you control.