My toilet flange is lifted by both bolts and I could smell sewer gas can I just screw the flange to the concrete or is there a repair flange I could get

What type of material is the closet flange and pipe? Pvc, cast iron, or copper. IF flange has lifted, you should be able to remove it(may take some work) and install a new one. If the flange has broken, you can indeed buy repair flanges and anchore them to the concrete. Can you post a pic of your flange so we can hopefully help point you in the right direction.

I too await pictures. You can't see this "my toilet flange is lifted by both bolts " with the toilet mounted. With the toilet unmounted you will for sure smell sewer gas. More details please