How can i change the PTR(Reversr DNS) for lightsail static IP ?

Thanks for using LIghtsail. The following document should have the info for you to config the reverse DNS on Lighsail instance

https://lightsail.aws.amazon.com/ls/docs/en_us/articles/amazon-lightsail-configuring-reverse-dns

I don't think you can do with with Public IPs in AWS. You can setup your own private hosted zones in Route 53 for reverse lookups of your private IP space (not valid for Lightsail which is a feature incomplete version of several AWS services focused on simplicity) but nothing for Public IPs that are owned by AWS and only temporarily allocated to customers.