Giving permissions to users/admins to various archives in Enterprise Vault is something that crops up as a request/question from time to time. You can, of course, go in to the Vault Admin Console, find the archive, and modify the permissions. Alternatively you can use EVPM, which is much more admin-command-line-friendly. Here is an article which explains the steps :
As an example, consider the following :
If I have a user called pj1, and I want to give my Vault Service Account permissions on the archive, before I start the permissions look like this :
I then put together the following .ini file :
SiteName=EV Site 1
GrantAccess = read, evvaultadmin
Run that, and now my permissions are as follows :
NOTE: In order to see the changes in permissions in the VAC, right click the list of Archives, and do a Refresh.