以下是使用Python解决这个问题的示例代码。该代码使用了pyyaml和boto3库。

import boto3
import yaml

# Get the secret
client = boto3.client('secretsmanager')
response = client.get_secret_value(SecretId='')

# Parse the secret string as yaml
try:
    secret_dict = yaml.safe_load(response['SecretString'])
except yaml.YAMLError as e:
    print(f'Error parsing secret string as YAML: {e}')
    exit(1)

# Access the values in the secret
username = secret_dict['username']
password = secret_dict['password']

# Use the values as needed
print(f'Username: {username}')
print(f'Password: {password}')

该代码从AWS secret manager中获取秘密字符串，并将其解析为yaml格式。如果解析出错，将打印错误信息并退出程序。秘密字符串中的值可以像字典一样进行访问，然后可以按需使用这些值。