while changing the homepage, i have lost the whole website

Can you please help me restore the changes.

I have done automatic backup using updraft. 

Sorry we do not provide support about 3rd Party plugins. But you can try the following troubleshoot things. 

1) Go to wp-admin >> Settings >> General and make sure Site URL and Home URl are same where WordPress is installed. 

2) If you want to change home Slug you should go to Pages >> Edit page and edit the slug. 

3) In case you want to change the Front page go to wp-admin >> Settings >> Reading and change the front page.

To turn on the revisions on page, edit the page and on top right click on Screens button. 

There select or check the box Revisions, now you have all previous edits there to to go back. 

If you lost your parent theme customization settings after activating the child theme, in that case you need to reactivate parent theme and use a plugin to download the customize settings so you can import them in child theme.