Ismay testified that he did not go anywhere that was not open to first class passengers until the time of the collision. Then he appeared on the bridge. However, he also said that he intended to examine more of the ship later in the voyage, in order to look for deficiencies.
He must have wandered around Olympic on one of her voyages. He requested changes to various things, including the mattresses, and ordered a potato peeling machine for the galley. As head honcho, he could please himself where he went.
>>but he could not tell the captin what to do that was not his place<<
Legally...no, he couldn't. However, this would be no barrier to "suggestions" and anyone making a habit of ignoring these "suggestions" did so at some risk to his career. Having said that much, there's little if any *direct* evidence that Ismay was as overbearing as some owners or owners representatives could be. That doesn't mean he wasn't or couldn't be, but for obvious reasons, that's not exactly the sort of thing he would 'fess up to on the official record *if* he was. Say what you will about Ismay and some have, he was not stupid.