You'll need a recertification.

What firms do when checking up CO2 bottles.
Visual check on the outside. No dents, cuts or other damage? (scuffed paint and such doesn't count)

If not damaged,
Put the bottle in a well padded bench vice. Support it over the full length. Undo the valve, put in an inspection camera. No corrosion or other anomalies on the inside.
Screw the valve back in. Using a torque wrench and the data that goes with the kind of bottle and valve.
Hydrotest it.

Clean up the bottle, restamp and repaint it, add warning stickers and such. Add bill.(probably more expensive than buying a new bottle)


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