The section in daml.yaml needs to look as follows:
scenario-service:
grpc-timeout: 60
This sets the timeout to 60 seconds. Note that for most projects there is no need to modify this. This only becomes necessary once projects grow very large.
You can find more information on the fields that you can use in daml.yaml at https://docs.daml.com/tools/assistant.html#project-config-file-daml-yaml