Two easy ways
get the Fiat check strap kit, it comes with a new roll pin, fluffy the impaler time...
Or drive out the old pin, but first tie a strong string to seat and to door so it does not open futher than normal, it will cause real damage otherwise. Replace with a large split pin, temporarily, which is easy to get, it desirably shouild be a resonable fit.
you need two hammers, one hammer wrapped with heavy rag, placed above pin carrier, other hammer hits pin from below..., or mole grips, one jaw wrapped in heave rag...
Take old roll pin to engineering shop and they will sell you a clone of the old roll pin, or give you one if you look poor enough.
Noel