One time only, open a command prompt, CD to your EPM Oracle Instance ("epmsystem1" by default), and then navigate to the folder where startcomponent.cmd / startcomponent.sh resides. This is pictured below for my testing sandbox.
startcomponent.[cmd|sh] ohs_component StoreUserConfig
This will ask for the WebLogic password (the same password you setup for the WebLogic admin user "epm_admin"), but now it will be saved behind the scenes so you'll never be asked again under the user account you're logged in as. The "StoreUserConfig" option at the end of the command is what does this for you.
Notice the command tells you the filename where the password was stored. If you have multiple people managing the system, copy that \.wlst\nm-key-ohs.props file from your home directory structure to theirs.
Having accomplished this, you may now add the startcomponent ohs_component command to your custom start-up script (you do have one, right?) to include OHS in your EPM start-up sequence.