Merging environment variables from secrets manager and local

Serverless Framework
,
1

I am using following for my service level environment which will be shared across functions.

environment: ${ssm:/aws/reference/secretsmanager/myServiceEnv~true}

How can I add additional env variables which are not in my secrets manager or something I want to generate through serverless opts? example:

environment: 
    TABLE_NAME: ${self:provider.stage}-${self:service}
    VAR2: "Value"

How to merge both so that I have secrets from secrets manager and additional variables provided in serverless.yml?

# outcome
environment: 
    SECRET: "From Secrets Manager" 
    TABLE_NAME: ${self:provider.stage}-${self:service}
    VAR2: "Value"

I tried merging yaml objects using tips provided in this post. I could not get it to work. Any snippets will be appreciated.