Delete flows in node-red
To delete flow in node-red,
- select the flow which you want to delete
- click on the right top corner bar
- select Flows -> Delete option
it will remove select flow from the node-red flows editor.
or you can follow the red circle area to delete the flow mentioned below the image.

Usefull Links
Read further tutorials if you are curious about node-red.
How to create multiple nodes in the node-red single module?
node-red environment variables example
I hope it helps you, All the best 👍.