Illustrative example
A tenant is shown a flat and told by the letting agent that the space by the side gate comes with it. The signed lease says nothing about parking, and after move-in the landlord allocates the space to somebody else.
Section 1625 makes the executed writing supersede the negotiations that preceded it, so a promise about parking that never made it into the lease is not a term of the lease. It turns on whether the parking was part of the same subject matter as the writing or a genuinely separate arrangement, and separately on whether the assurance was false when it was made, which is a fraud question under sections 1572 and 1710 rather than a contract one.
The landlord provides an alternative space, or a rent reduction equal to the local cost of parking for the rest of the term, recorded as a written addendum to the lease.