How to create mongo container with my python app container inside same pod in kubernetes cluster

I want to migrate my in kubernetes cluster and created my own clusters manually. I have made an app in python and connect it with mongoDB using the official mongo image mongo. it works fine in docker compose because after creating container i manual enters the mongo container and make replicaSet and user of my choice after my service start working. but when i shift my service to kubernetes deployment and make 2 or 3 replicas of deployment then i have to initialise mongo by doing to every pod one by is there any way to automate the mongnoDB container that can automatically set the user name and password and replicaSet as well.