After changing my domain, per the directions, I'm no longer able to access the Lightning AppBuilder.  It pops up a new authentication window where my password no longer works.  I tried using the custom domain link but my username and password still don't work.  So I can get to salesforce setup but not to the lightning appbuilder to complete the exercise....

Changed my domain as directed by the exercise.  I'm able to log into Salesforce but when I now go to the Lightning AppBuilder through Setup it pops up a new authentication window where my username and password no longer work.  So I can't get to the Lightning AppBuilder to complete the exercise.  I've tried using the Custom Domain link at that new authentication pop up but no luck, my password still doesn't work.  

I need to delete a Wave Dataset(s) but I can't do that because the dataset is associated with a Dataflow.

Thus, I need to delete the Dataflow; however, I'm unable to do so??

There are no instructions for doing so and one unable to upload a blank json file to replace the existing Datflow?

I need help with this specifically, since the datasets put me over my storage limit and prevent completion of other Trailhead trainings.  However, more generally there should be a simple delete Dataflow function, as other users have mentioned.

I need to delete a Wave Dataset(s) but I can't do that because the dataset is associated with a Dataflow.

Thus, I need to delete the Dataflow; however, I'm unable to do so??

There are no instructions for doing so and one unable to upload a blank json file to replace the existing Datflow?

I need help with this specifically, since the datasets put me over my storage limit and prevent completion of other Trailhead trainings.  However, more generally there should be a simple delete Dataflow function, as other users have mentioned.

Does anyone know why I am getting this error, when the process clearly exists and is active?

Challenge not yet complete... here's what's wrong: 
There was an unexpected error in your org which is preventing this assessment check from completing: System.DmlException: Process failed. First exception on row 0; first error: NO_APPLICABLE_PROCESS, No applicable approval process was found.