Steps:
Find IAM AWS service
Choose ‘Users’ -> ‘Add users’







Provide name of policy and finish policy creation
Refresh policies list on page of user creation and find your policy.

Create credentials to execute lambda:
Find the user in IAM and click to it
Choose ‘Security credentials’



Click ‘Next’ -> ‘Create access key’
Save your ‘Access key’ and ‘Secret access key’

Useful links: