How can I restore my iPhone backup?

I backed up my mobile to my laptop using iTunes but my laptop has completely stopped working.

The iPhone 7 Plus storage -> 32 GB, 128 GB or 256 GB

Have you check the space on your computer before doing the back up?

How can I restore my backup now.?

Think you need to get enough free space on your laptop first.

Or make a back up to iCloud, see this Apple article: How to back up your iPhone, iPad, and iPod touch

How to back up your iPhone, iPad, and iPod touch - Apple Support

The backup is saved to your hard drive, not in iTunes. See→Locate backups of your iPhone, iPad, and iPod touch - Apple Support

Then you can’t restore the backup from your laptop. Did you also back up to iCloud?