How to Wait for the AWS Service to Finish Batch Processing before Starting Another Batch

There is a batch A running on Lambda started by the timer rule of Cloudwatch Event. There is another Lambda batch processing B that I would like to do after Lambda is finished.
Up until now, B was called asynchronously in Lambda.invoke of aws-sdk

I want to do it after A next time, but I can do another batch process called C which is not dependent on B.
You can write a code that invokes C at the end of A, but
It's hard to ask for corrections every time in another department that manages A. I was asked to create something like a trigger event
Subsequent batch processing begins as if you were looking at the event.
I want to be able to add follow-up actions without changing the before and after batches

Isn't there a service that AWS can do that?

In addition to timer rules, CludWatchEvent also has events that trigger S3PUT. At the end of A, have S3 leave an empty object
I don't mind triggering that event, but
Is there a way to ignite the event itself more directly or a sample code like that?