If you're still in undergrad, the fix is an upward trend: take genuinely hard upper-division science courses and do well in them, since a clear trajectory matters more than an early stumble. If you've already graduated, you're generally choosing between two structured paths.
A DIY or formal post-baccalaureate program adds undergraduate credits and directly raises your cumulative GPA over time. An SMP puts you in actual medical-school-level coursework to prove readiness — it won't move your undergraduate GPA at all, but a strong performance can matter more to admissions committees than GPA repair would have. SMPs are genuinely high-stakes: performing poorly in one is a significant red flag rather than a neutral attempt.