hope everyone confuses with placeholder and constant.
Assume having a db with name d6u5qhrlnbdfmp. then it is NOT necessary to type
heroku pg:reset d6u5qhrlnbdfmp
Instead we can plainly type
heroku pg:reset DATABASE_URL
the sample output
E:\git\stutzen>heroku pg:reset d6u5qhrlnbdfmp --app stutzen
! Unknown database: d6u5qhrlnbdfmp. Valid options are: DATABASE_URL, HEROKU_
POSTGRESQL_CYAN_URL
E:\git\stutzen>heroku pg:reset DATABASE_URL --app stutzen
! WARNING: Destructive Action
! This command will affect the app: stutzen
! To proceed, type "stutzen" or re-run this command with --confirm stutzen
> stutzen
Resetting HEROKU_POSTGRESQL_CYAN_URL (DATABASE_URL)... done