Hi SA-MY, you can do that within the IAM (Identity and Access Management) service. Once there, choose Policies, click the 'Create Policy' button and then select the JSON tab, where you can paste the policy details in.

You will also need to link that policy to whichever EC2 instances will be performing certificate management activities via LetsEncrypt. Best is to create a Role, then assign the policy to the Role and the Role to the instance.

Hope that points you in the right direction!