Smooth and store used gift ribbon
Smooth used ribbon according to its material, then store it loosely rather than assuming every kind can be ironed.

Open the knot and identify the material
Undo old knots gently with your fingers. Do not pull one end if that only tightens the knot. A short cut may be better than preserving a long piece that becomes badly damaged in the process. Remove tape and check for sticky residue underneath.
Distinguish textile ribbon from paper, plastic and metallic-coated gift strips. Wired edges need separate consideration too. If the material is unknown, start without heat. A shiny ribbon may melt or lose its surface against a hot iron.
Trim frayed ends only after deciding the needed length. An angled cut looks neat but does not stop every material from fraying. Do not use an open flame to seal unidentified ribbon. A small turned end may be enough for a gift bow if it does not create excessive bulk. If damage sits in the middle, divide the ribbon into two sound shorter lengths and record them rather than hiding the weak area inside a roll.
Begin with the mildest treatment
For a gentle curve, lay the ribbon between clean paper sheets under a light weight. Textile ribbon with known care information may be pressed accordingly. Test a discreet area first, and do not raise the temperature simply because an old fold remains visible.
Straighten wired edges carefully with your fingers, avoiding repeated bending that can break the wire. Remove or discard a section with a hard exposed point. Paper ribbon does not need to become perfectly flat to work again as a short bow.
Store without creating new creases
Wind longer pieces loosely around broad cards or a suitable spool. A tiny winding diameter immediately creates tight new curves. Secure the end with a loose loop or tuck it beneath a turn rather than applying strong tape to the visible surface.
Record approximate length and width if you hope to use it for several matching gifts. Keep short pieces together in a shallow compartment. Store only clean, dry ribbon and keep unknown coatings away from food. An old fold may disappear visually within a bow; it does not need aggressive treatment before the ribbon can be useful again. Choose its next job around the sound length that remains instead of stretching or heating it to recover every fraction of the original piece.