Fetch Secrets Manager secret cross account

I’m having two accounts, let’s call them A and B.
In account A I have a secret in Secrets Manager. I would like to read this secret in account B’s serverless’ file.

If only one account I’m populating environment variables in my serverless.yml file in this way:
custom: secrets: ${ssm:/aws/reference/secretsmanager/test-secret-in-account-A}
I then populate an environment variable using:
provider: environment: AUTH_TOKEN: ${self:custom.secrets.token}
This works perfectly if all within one account. But how can I read a Secrets Manager secret hosted in account A in account B?
Thank you!