This question is an exact duplicate of:
Currently, if one wants to give a user special access to a room, one must know the users chat id. As a moderator, I can easily create a chat user for someone who doesn't have one (via superping), but I can't find it easily.
As mentioned in the update on the question I linked to, one needs to know the chat ID to provide access. This is rather cumbersome to do when you don't know the chat ID (but do know an SE profile)
I propose this:
In the "grant user access" area, allow the profile to be entered in
<site>.stackexchange.com/users/<userid> form as well as the standard chat.se user ID.
If this will lead to rather heavy queries, at least let
<parent-site>.stackexchange.com/users/<userid> work—in most cases you already know the parent user (when you use the superping), or can make a good guess (the user has only a few accounts)