urgent . error in gstr 3b and tax paid for july

what is the remedy available if I have paid tax at higher rate of 18% and also filled gstr 3b. but now I came to know that it should be charged at 5% and also the service recipient is asking me to revise the bill. can I rectify my return through gstr 1 and 2. please explain me the process and also how excess tax will be adjusted or where will it be reflected in my profile