Need a new retainer. In most cases, dentists are able to match the original anatomy of a tooth when fabricating a crown so that the invisalign retainer fits. However, this is not possible in all cases. The invisalign retainer cannot be manipulated to fit the new crown, as attempts to do so will distort it, with negative consequences. Consult your dentist/orthodontist to have a new retainer fabricated.
You Can't. More than likely you can't. See your dentist.
See dentist. A new retainer from a new model may be needed.
New trays. Have your orthodontist take new impressions and order new trays for you.
Need new one. As the finish of a clear aligner case is most often not as finely tuned as a braces case, it's harder to maintain post-treatment stability for aligner cases. I've not been pleased with the results when trying to retro-fit a clear tray retainer. Better to take a new impression and make a new retainer.