how can be changed hot_standby parameter on postgres 9.6 aws/rds?
Ideally the parameter hot_standby should be on only for slave server and pg_is_in_recovery() should be false for master server. 

You can follow below steps to make these changes:  


Check postgresql.conf file on master server and if the parameter hot_standby is set to on you can change it to off and then restart the server.  
On the master server in the data file location, if there is a file called recovery.conf then just delete that file and restart the server. 


Hope this will help.