To reset your DNS zone files to the defaults:

Reset Zone files

Warning: This feature will erase any modifications you have made to your zone records, either using this feature or using the Simple DNS Zone Editor. It will attempt to save TXT entries. Before using this feature, be sure to write down any changes you may want to save.

Find "Advanced Zone Editor" under "Domains" Category in cPanel. 

1.    Select a domain from the drop-down menu.

2. Click "more" at Reset Zone File part.

3. Tick the check box next to "Are you sure you want to erase all entries and revert to the default state"?

4. Click "Reset Zone File".