I want to enable a disabled input format I considered 'restricted HTML' as unnecessary and set it ‘disable’.
Because I thought it possible to re-enable.
However, I have not found a disabled format on UI.

Since there is no choice, I decided to newly register.
The same registration as the default machine name 'restricted_html' conflicts.
Imagine the data is left somewhere.
I could not find it even if I looked for a database.
Is it possible to restore by setting file or something?

I am using Drupal 8.4.2.
This is a known issue, though you are warned before you disable the textformat that this cannot be undone. See the issue Disabled text formats can't be seen in the GUI and the comment #60:


  It is possible to reenable disabled text formats with the
  configuration manager:
  
  
  go to /admin/config/development/configuration/single/export
  choose Text format as the Configuration type
  choose the disabled text format as Configuration Name
  copy the configuration
  go to /admin/config/development/configuration/single/import
  again choose Text format as the Configuration type
  paste the configuration
  change "status" from false to true
  click on import
  
  
  Voilá, the text format is available again. This is working but not
  user friendly :(