Grafana dashboard Drop downs

I have grafana dashboard for node-exporter 0.16, and i have filters region and name as dropdowns.
Based on the region drop down,(eu-west-1a/1b) its corresponding names would appears, which works just fine.

I have new requirement, where i need to introduce new drop down Environment, which has drop down values as PROD,UAT.
So total 3 dropdowns
Region Environment and Names.
Now the issue am facing is below:
Chosse region(eu-west-1a), corresponding available enviornments (PRD.UAT) displays fine.
But, when i choose UAT, its corresponding names are not being reflected in Names drop down.
I have metrics defined as below:
$job node-exporter as a constant
$region label_values(node_boot_time_seconds{job="$job"}, region)
$env label_values(node_boot_time_seconds{region="$region"}, env)
$name label_values(node_boot_time_seconds{job="$job",region="$region"}, name)

Basically I choose region, based on it, its displaying environment, but based on environment, its not changing the names of apps, instead it reflecting the names based on region.

Thanks in Adv