This assumes you have already configured the aws command line tool. If not, check out my article on Getting Started with the AWS CLI.

The aws ec2 describe-instances command can be used to list your EC2 instances.

aws ec2 describe-instances

--filter can be used to only return the JSON for an specific instance.

aws ec2 describe-instances --filters "Name=tag:Name,Values=my-instance"

Something like this should be returned (this is just a small subset of the output that would be returned). Notice in this example that the EC2 ID is i-09112345cf1abcdd2 and currently has 1 tag (Name = my-instance).

{
    "Reservations": [
        {
            "Instances": [
                {
                    "AmiLaunchIndex": 0,
                    "ImageId": "ami-09d123474b6cabcda",
                    "InstanceId": "i-09112345cf1abcdd2",
                    "InstanceType": "t2.micro",
                    "KeyName": "aws",
                    "LaunchTime": "2022-11-06T09:23:52+00:00",
                    "Tags": [
                        {
                            "Key": "Name",
                            "Value": "my-instance"
                        }
                    ]
                }
            ]
        }
    ]
}

The aws ec2 delete-tags command can be used to delete tags from an EC2 instance.

aws ec2 delete-tags --resources i-0d4b6d80b3763f894 --tags Key=Name