WordNet records no synonym and no antonym for relearn. It is the only member of its synset, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
learn something again, as after having forgotten or neglected it
“After the accident, he could not walk for months and had to relearn how to walk down stairs”
Synonyms, antonyms and the broader and narrower relations for relearn come from Princeton University’s WordNet. Full sources and licences.