Phase 1a/1b dose escalation and expansion study designed to evaluate the safety and tolerability of NVL-330, determine the recommended Phase 2 dose (RP2D), and evaluate the antitumor activity in participants with advanced or metastatic human epidermal growth factor receptor 2 (HER2) -altered non-small lung cancer (NSCLC). Phase 1a dose escalation is designed to assess the safety and tolerability of NVL-330 and to select the candidate RP2D(s) and, if applicable, the MTD. Phase 1b expansion is designed to further evaluate the overall safety and tolerability of the candidate RP2D(s) of NVL-330 and to determine the RP2D of NVL-330 in participants with advanced or metastatic HER2 mutant NSCLC.