Step 1: Do cmd + R
Step 2: Type %appdata%
Step 3: Then click enter. After you click enter there should be a file named ".minecraft"
Step 4: Double click on ".minecraft"
Step 5: Now you are going to scroll down to "versions"
Step 6: Double click on that and now all you have to do is right click on the version that is not working then click "delete" *make sure you left click it once*
I hope this helped you!
