Adjusting the belt is occasionally necessary. Despite lubrication, belts sometimes shrink up with age. In which case, occasional loosening is needed.
There's a hex adjustment key that comes with the treadmill. It generally fits into a hole near the part of the treadmill that you face away from while you are on it. You turn it in that hole, to adjust the tension of the running belt. (Your model may differ, of course.)
As for lubricating those springs... springs will squeak, if you're using the treadmill heavily, and/or if you're a well-built bodily type.
If those springs are well-separated from the running belt, not adjacent to it either as the belt passes on the upper side, nor adjacent to it as the belt passes on or near the lower side of the running platform, then lubricating them might be the first thing to try. A grease lubricant for moderately heavy machinery, applied to the upper part of the springs, might help - provided that there also is no rubber gasketing nearby in this model, otherwise the grease might get on the rubber gasketing and decay it.
Does this answer your question adequately and completely?