How can I restore from a specific backup in iPhone?

You can do that restoring the iPhone in the iCloud or with a PC/iTunes or a MAC in Finder, when you start the restore process you are aked to choose a backup, it's a scroll with all the backups you made, you can then select the one you like. Follow the guide

Restore your iPhone, iPad or iPod touch from a backup – Apple Support

Remember that iTunes only saves one backup per device. Every time you back up again, you overwrite the last backup. The exception to this is that backups on a Mac can be archived and you can have multiple backups. If you use a Mac that runs Catalina or higher and you backup via the finder, the same applies about archived backups.

iCloud should save two backups for each device. So you would only have access to one of those backups.

If you want to restore an iCloud backup from some time ago and you backup every day, those backups are gone. For instance, if you want to use a backup from October and you have backed up twice in November, that October backup is gone.