I need to change the stack from Dot Notation to Ubuntu

[ZacharyGaston]

Hi. I created a new workspace and I'm trying to change the stack from dot notation to Ubuntu. I clicked on the cog to configure settings but I don't see where I'm supposed to go as the next step. I thought it was environmental variables but it's asking me to: "Add/Edit environment variables by changing the environment type to compose" and I don't see where I should be clicking on to do that. If anyone has any tips, please message me at your earliest convenience.
Reproduction Steps:
Created workspace