How to regain muscle ?

After being on prednisone on and off for 8 years, now currently taking kevzara and at 2.5 mg of prednisone. I attempted to see what my walking ability is. Before this, I would walk a mile in 20 minutes. (At 62) now I'm 70, and I was barely able to do 5 laps in my driveway (approximately 1/4 mile) in 10 minutes. And I was done, straight to my recliner. How in the world do I get any of my original back ? (Knowing those 8 years of age is a big factor)