Merchant Export by a manufacturer

A manufacturer is seeking clarification on GST implications for merchant exports. They charged IGST at 0.1% and claimed full ITC at 18% on inputs. The core question is whether they must reverse the proportionate ITC or if the excess ITC can be offset against liabilities from other regular outward supplies. Advice suggests exploring a refund application if ITC was paid on export goods, contingent on GSTR 2A/2B reconciliation and valid LUT.