My backyard stairs are concrete and the railing has been getting loose. I can now move it.
What should I do to fix it? Do I need a professional?
Optionally apply a sand/epoxy mix over the anchoring cement to give it a coordinating appearance and prevent degradation by weather. Over time rain and wind will wear it away as it's relatively soft.
Obviously this repair is only as good as the condition of the stairs. If the crack we see is indicative of the shape the rest of the stairs are in, you may need to have them removed and re-poured.