Why thanks @MyrtleStrumpet! I use microsoft designer
https://designer.microsoft.com/home
I have discovered a way to edit the instructions using the "prompt template" (opens via link, you edit it, and then close it, and then press "generate") but it is far from infallible and I don't really understand how the prompt template works.
The first image shows a prompt template, the second image is what it gave me, the third image is when I modified the prompt to add tunnocks tea cakes with silver and red [foil wrapping]. But with that, I didn't get the gerbil waiter I wanted ...