AWS SAM to use existing event bridge rule to trigger lambda

Question

I am using SAM to create few AWS resources like Lambda. I am using amplify to create S3. I need to create a eventbridge rule to trigger lambda whenever a file is uploaded to S3. But I have 2 issues:

1. I am not able to create eventbridgerule using existing S3 (which is already created using amplify). I used the below code and I was not successful. Is there a way to use existing S3 bucket in SAM?

MyLambda:
    Type: AWS::Serverless::Function
    Properties:
      FunctionName: 'MyLambda123'
      CodeUri: code/
      Handler: lambda_function.lambda_handler
      Runtime: python3.7 
      Policies:
      - Statement:
        - Sid: SSMDescribeParametersPolicy
          Effect: Allow
          Action:
          - ssm:DescribeParameters
          Resource: '*' 
      Events:
        Trigger:
          Type: EventBridgeRule          
          Properties:            
            Pattern:
              source:
                - "aws.s3"
              detail:
                bucket:
                  name: 'someexistingbucket'

2. I went ahead and created eventbridge rule manually. I know we can create a new eventbridge rule using SAM. But how can I use an existing eventbridge rule to trigger lambda function.

MyLambda:
    Type: AWS::Serverless::Function
    Properties:
      FunctionName: 'MyLambda123'
      CodeUri: code/
      Handler: lambda_function.lambda_handler
      Runtime: python3.7 
      Policies:
      - Statement:
        - Sid: SSMDescribeParametersPolicy
          Effect: Allow
          Action:
          - ssm:DescribeParameters
          Resource: '*' 
      Events:
        Trigger:
          Type: EventBridgeRule    
      
 ##Somehow I need to know how to use existing eventbridge rule (which I created manually)##