The first proofs were non-constructive, by way of contradiction.[2]
Later, constructive proofs were found, which also supplied algorithms for finding the complementary edge.[3][4] Basically, the algorithms are path-based: they start at a certain point or edge of the triangulation, then go from simplex to simplex according to prescribed rules, until it is not possible to proceed any more. It can be proved that the path must end in a simplex which contains a complementary edge.
An easier proof of Tucker's lemma uses the more general Ky Fan lemma, which has a simple algorithmic proof.