Hello! You might've seen the notification, but I was told you may be able to help me with something regarding a Pokemon I'm looking after from the Great Crater of Paldea? In an effort not to continue sending the original poster notifications I thought I'd just send this directly to you, haha! ( @malus-pokemon-research )
AH- Yes, I have caught up on my notifications and done a quick readthrough. From my understanding of your situation, a friend has entrusted an Iron Valiant to you to look after for a period of time, and you are concerned about its perceived shyness. Correct?
Given the nature of my specific research, I am usually inclined to start with a warning. The Pokemon from the Great Crater have been observed to be EXTREMELY VOLITIALE and PRONE TO ATTACK at little to no provocation. They are not all so extreme, but it is EXTREMELY common for them to be for a variety of reasons.
However, given the context of the situation presented, I will assume that your friend has made the good judgement that the Iron Valiant is not one likely to lash out. STILL, I would caution you to exercise common sense and not try to FORCE it to do anything it does not seem to want to do.
NOW THEN. In my observation of my own Iron Valiant and the others I've been able to study, even ones that are not particularly aggressive do still enjoy being given an outlet to fight. It might enjoy being given a space to practice its swordsmanship, and if any of your Pokemon are strong enough to fulfill the role, it might enjoy a sparing partner as well. This is a good way to bond with it and might help it be more open.
Objects which challenge their wit are also something Iron Valiant seem to enjoy. Many toys for psychic type enrichment are also enjoyed by Iron Valiant. This likely won't DIRECTLY help with openness, but is a good for its Quality of Life.
Otherwise, Iron Valiant are, for the most part, somewhat reserved, so set reasonable expectations for just how openly it will behave. The most obvious tell that an Iron Valiant has taken a particular interest in something is an intensity in the glow of their eye-lights, and is something to look out for when trying to find things one enjoys. Iron Valiant will also only sleep sitting or laying down if they feel completely safe in their environment, so if you notice that, it likely is more comfortable around you than you think.
If there is anything else of note you have observed while caring for the Iron Valiant I might be able to give more specific feedback, but this is the best I can offer from what I know of your situation currently.