Manual for installing Retool on AWS

I would just like to try Retool.

Get started with Retool self-hosted for free
I select:
One click deploy
text: "You will only need to choose your VPC and SSH key-pair to get started."
I click "Launch Stack" (after signing up to AWS).

VPC: I can choose something AWS created.
licenseKey: already filled out by Retool.
retoolKeyPair (Key pair to access the box running Retool): nothing can be selected/typed in.
Trying to create stack on AWS results in faliure/rollback
"Parameter validation failed: parameter value for parameter name retoolKeyPair does not exist. Rollback requested by user."

There's nowhere to enter this retoolKeyPair - and where do I find/get it?

Isn't there a manual for this?