This is a example setup based on the sample-chart.
In case you use an chart from a registry you can omit the chart related folder.
But as you need to overwrite the charts values.yaml you would need to create a new file with the properties for overwriting the exiting values.
In this example we have two files, for each environment one.
Beside that we have a .sealit.yaml which contains the configuration.
The environment variables will be mapped to a ConfigMap and a SealSecrets resource.
helm update -i sample ./sample-chart -f values.dev.yaml
helm update -i sample ./sample-chart -f values.prod.yaml