If the letter of recommendation from your supervisor is weak or doesn't effectively showcase your skills, speak with your supervisor to see if there's anything you can do to improve the letter. You can provide additional information or materials that may help your supervisor write a better letter or offer to schedule a meeting to discuss your skills and accomplishments in more detail. If this isn't possible or doesn't result in a stronger endorsement, consider reaching out to another individual who can provide a stronger recommendation. Be sure to thank your supervisor for their time and effort regardless of the outcome, as maintaining positive relationships is essential in any professional setting.