With Multiple PUM environment on a host, how can I set environment variables automatically at login?

With Multiple PUM environment on a host, how can I set environment variables automatically at login?

We have got 4 PUM images on a single host. Everytime we install a PUM image, the environment for that image is set. And so, we need to manually set environments for the already installed PUM images.  e.g. psadmin shows domains for only the last PUM image. To see previously installed image app/web/prcs domains, i need to manually set some environment variables.....

I think there are some bash statements that can be set in environment files at login and they ask which environment do you want to go to? And then, it sets the environment based on what we choose.