Hi Florent! Looks like a nice, healthy tree. As for your question, there are a couple of ways to respond.
Timing wise, now is a good time to work on the tree, though if you do significant bending you’ll need to protect the tree from hard freezes, if any, during winter.
As for what to do with the tree, do you have an idea of what you want the tree to become? If you want the trunk to become larger, then the tree will need to grow for several years. If you’re happy with the trunk then you can start any time.