Register in an LMS the highest score of 2 possible attempts

You can apply that JavaScript from anywhere in your course. But likely it would make the most sense to have a final/last landing page from where you can trigger the JS to set the final score.

// get LMS API
var lmsAPI = parent;

// set score; the first number is the score
// lmsAPI.SetPointBasedScore(intScore, maxScore, intMinScore);
lmsAPI.SetPointBasedScore(yourVariableHere, 100, 0);