Can the US President overturn Supreme Court decisions?

No. US Supreme Court decisions are final unless Congress and the States ratify an amendment that effectively changes the Court's ability to rule on certain issues; or the Court agrees to a rehearing based on new information; or (more common), a later Supreme Court may have a different constitutional interpretation than an earlier court, resulting in a decision on a new case that changes nullifies laws or changes how they are applied.

Once common example is the case of Brown v. Board of Education, (1954), ended segregation allowed n public schools under the doctrine of "separate but equal" that arose from the an earlier Court's decision that the practice of racial segregation was constitutional as long as the accommodations were equal (they weren't).