I want to remove RDS's DB replication settings and change it so that the current reader instance performs all reader/writer tasks.

Currently, I am using mysql in rds with two instances of reader and writer, but I would like to remove the writer instance and set the reader instance to read/write. This is an attempt to reduce costs. Actually the usage is not high enough to require DB Replication. Due to circumstances, the DB connection address of the current reader instance must be maintained. Therefore, I would like to remove only the writer instance and set the reader instance to enable writing as well. I would like to know how to do this. please answer about my question.