For a sprained and swollen foot, especially for an elderly person, it's important to follow the R.I.C.E method at home:

Rest: Avoid putting weight on the affected foot to prevent further injury.
Ice: Apply ice packs to the swollen area for 15-20 minutes every 1-2 hours to reduce swelling.
Compression: Use an elastic bandage to wrap the foot snugly, but not too tight, to help reduce swelling.
Elevation: Keep the foot elevated above the level of the heart as much as possible to decrease swelling.
If the swelling and pain persist, or if you're concerned about the injury, it's important to seek medical attention to rule out more serious issues.