you cannot cook formula milk but you can add the prepared formula to the dish once its room temperature.. However cow's milk is fine. why are you trying to avoid cow's milk ??

Yes you can add fruits to add the sweetness. Avoid sugar. Cook the rice or sooji with water and once fully ready and ready to serve mix in the formula. I would ideally recommend starting sooji a little later as it is wheat and instead trying ragi.

also can I mash fruits to it for sugar content .l as I want to avoid sugar . so which fruits I should add and how

I mean please share recipe for suji or rice kheer and tell weather formula can be added as I want to avoid cows milk