If the loose part is only the decorative front name ring, the practical fix is to remove any old residue or corrosion so the mating surfaces are clean, then bond it back in place carefully. In the reported case, super glue was used successfully after cleaning away the yellow powder and preparing clean metal surfaces.

Use great caution: adhesive near the front element or threads can permanently damage the lens, create fumes that leave residue on glass, or make future servicing difficult. Apply only a very small amount, keep it away from optical surfaces and moving parts, and align the ring before it sets.

If the loose screw is structural rather than cosmetic, that is a separate issue and should be handled carefully before relying on the lens. If you are not comfortable risking the lens, a camera repair technician is the safest option.