First, install the AWS PowerShell module on PowerShell 5.0 or later:

Install-Module -Name AWSPowerShell -Scope CurrentUser -Force

Now, go to the IAM console and generate an access key, and use the following command to set your credentials in PowerShell.

$AccessKey = '<YourAccessKey>'$SecretKey = '<SecretKey>'$Region = 'us-west-1'Initialize-AWSDefaults -AccessKey $AccessKey -SecretKey $SecretKey -Region $Region

Now that you're authenticated from PowerShell, use the following one-liner script to pop open a list of EC2 instances in a WPF window, and select the ones you want to tag.

(Get-EC2Instance).Instances |   Out-GridView -OutputMode Multiple |   ForEach-Object -Process {     New-EC2Tag -Tag (New-Object -TypeName Amazon.EC2.Model.Tag -ArgumentList @('Key', 'Value')) -Resource $PSItem.InstanceId  }

PS command

New-EC2Tag -ResourceId $Instances -Tags $Tags

From AWS documentation....

$tag = New-Object Amazon.EC2.Model.Tag$tag.Key = "myTag"$tag.Value = "myTagValue"New-EC2Tag -Resource i-12345678 -Tag $tag

Need to add more than one tag!

$Tags = @()

$1T=New-Object Amazon.EC2.Model.Tag;$1T.key="KEYNAME";$1T.Value="VALUE";$Tags += $1T$2T=New-Object Amazon.EC2.Model.Tag;$2T.key="2ndKEYNAME";$2T.Value="2ndVALUE";$Tags += $2T$3T=New-Object Amazon.EC2.Model.Tag;$3T.key="3rdKEYNAME";$3T.Value="3rdVALUE";$Tags += $3T$4T=New-Object Amazon.EC2.Model.Tag;$4T.key="4thKEYNAME";$4T.Value="4thVALUE";$Tags += $4T$5T=New-Object Amazon.EC2.Model.Tag;$5T.key="5thKEYNAME";$5T.Value="5thVALUE";$Tags += $5T

New-EC2Tag -Resource i-12345678 -Tag $tag