Get list of instances in the VPC:
[evan@Evan ~] $ aws ec2 describe-instances --filter Name=vpc-id,Values=vpc-id | jq '[.Reservations[] | .Instances[] | .InstanceId ] | join(",")'
Get the list of volumes attached to those instances:
[evan@Evan ~] $ aws ec2 describe-volumes --filters Name=attachment.instance-id,Values=i-abcd,i-abce,i-abcf,i-abcg
Paste result into this command:
[evan@Evan ~] $ aws ec2 create-tags --tags Key=environment,Value=production --resources vol-abcd vol-abce vol-abcf