How you reseal stamped concrete will depend on the type of concrete sealer currently down, and what you want the stamped concrete to look like once sealed.
Best Practice Tips For Reapplying A Concrete Sealer On Stamped Concrete
Water Based Acrylic Sealer: If the stamped concrete is currently sealed with a water based acrylic sealer, it is best practice to maintain the surface by reapplying with only a water-based concrete sealer. You can't apply a solvent based acrylic sealer over a water based acrylic sealer because the solvents will chemically react and attack the water based product, resulting in coating failure. The only way a solvent based acrylic sealer can be applied to stamped concrete previously sealed with a water based acrylic is if the water based acrylic sealer has been completely removed. Water based acrylics will provide a low to high gloss finish without enhancing or darkening the color of the concrete.