1. Update items using the update-item command:

aws dynamodb update-item 
    --table-name my_table 
    --key '{"id":{"S":"001"},"dateandtime":{"N":"1536898265"}}' 
    --update-expression "SET field1=:field1" 
    --expression-attribute-values '{":field1":{"N":"30"}}' 
    --region us-east-1
    --profile admin

For update-item, you need to specify all the keys available using the key option.