Create a metric filter in the selected log group for 'ERROR' and link it to an alarm that triggers the SNS topic when the metric exceeds 1.

Utilize CloudWatch Logs Insights to create a metric query for 'ERROR' and set an alarm for the metric to alert the SNS topic when it hits 1 or more.

Establish an SNS subscription filter for 'ERROR' within the selected log group, directing notifications to the SNS topic.

Formulate a CloudWatch alarm with 'ERROR' as a filter, using the correct log group, to alert the SNS topic upon occurrence.