It is unlikely that you can do anything in the camera settings to improve the situation. Some cameras have a "boost mode" which improves performance at the expense of battery life, but most — including yours — don't, and it's not like you can just add such a feature.
If you're not using the camera's AF assist light, you could turn that on. Presumably, you are either already doing that and still unhappy — or want to avoid blinding your subjects.
That leaves you with three choices:
- Improve the situation. Add light or contrast. This could be as simple as turning on the room light or introducing something with hard edges into the scene.
- Try a hotshoe flash with AF assist beam. I believe your camera just uses a regular LED, whereas many external flashes offer a much less intrusive IR beam — which you can use even when not using the flash itself.
- Upgrade your camera... autofocus speed is still an area where new models offer constant improvement.