How can one get rid of a bad reputation?

Your question is general, and a specific answer cannot be given, but in general:

1. Remove the cause of the bad reputation by avoiding evil, doing good, being upright, and staying away from misguidance.

2. Avoid situations of suspicion.

3. Choose your companions: associate with the good and stay away from the wicked.

4. You must supplicate and ask Allah for well-being from every affliction.