GST paid and return filed with the wrong gst rate

If taxes are erroneously paid in excess in GSTR-3B, the same can be claimed as a refund (as per Section 54 of CGST Act) or be adjusted against tax payments of subsequent periods. But, the same cannot be claimed though GSTR-9. The refund needs to be claimed by making an application for the same on GST portal. 

You can make changes until you submit the GSTR-9. However, once submitted, you can not make any changes in GSTR-9.