From the photos, we assume the main problem you want to address is that the shrub has fallen over. The roots appear to still be in the ground, which is good. Don't let the roots get exposed to air and dry out. If you cannot do something immediately, at least cover the upheaved base of the shrub with soil so the roots do not dry out.
When shrubs or trees lodge (fall over), some roots are broken by the fall. Even if you can pull this shrub back into its original upright position and stake it (no more than a year), it may have lost so many roots that some of it will die. But, if it has enough healthy roots left, it will put out new growth.
If you want to save it, pull it up and stake it for a while. Be sure it has enough water for the next two years. In winter, when there is little evaporation from the soil, watering is usually not necessary (and you can't water when the ground is frozen anyway.) Spring through fall, however, water when it gets less than 1" of rain a week or the top 1" of soil dries out.
Prune off any dead branches.
Photinia usually gets leaf spot diseases (caused by fungus.) Clean up fallen leaves and dispose of them in the trash.
Do not over-fertilize. It will stress the shrub.
Once the plant's roots seem to be secure and it is putting out new growth next year, then you can consider cutting it back by 1/3 each year to keep it bushier.