I have multiple mongoose schemas referenced into each other. I am using gql-compose-mongoose. How to push the objectID of one document into other?

Question

I am creating a gql express server and i have created multiple schemas and referenced those schemas into each other. Assume collection USERS. Each user will have multiple challenges(schema or collection - challenge). I want to store the document(challenge) id into an array of challenges inside the user document that created it and vice-cersa.How can I acheive this?

My user Schema -

import mongoose from "mongoose";
import { composeWithMongoose } from "graphql-compose-mongoose";
const { Schema } = mongoose;
export const UserSchema = new Schema(
  {
    name: {
      type: String,
      trim: true,
      required: true,
    },
    email: {
      type: String,
      lowercase: true,
      trim: true,
      unique: true,
      required: true,
    },
    challenge: [
      {
        type: Schema.Types.ObjectId,
        ref: "Challenge",
        required: true,
      },
    ],
  },
  {
    timestamps: {
      createdAt: true,
      updatedAt: true,
    },
  }
);

export const User = mongoose.model("User", UserSchema);
export const UserTC = composeWithMongoose(User);

My challenge Schema -

import mongoose from "mongoose";
import { composeWithMongoose } from "graphql-compose-mongoose";
const { Schema } = mongoose;
export const ChallengeSchema = new Schema(
  {
    user: [
      {
        type: Schema.Types.ObjectId,
        ref: "User",
        required: true,
      },
    ],
    task: {
      type: String,
      trim: true,
      required: true,
    },
    description: {
      type: String,
      trim: true,
      required: true,
    },
  },
  {
    timestamps: {
      createdAt: true,
      updatedAt: true,
    },
  }
);

export const Challenge = mongoose.model("Challenge", ChallengeSchema);
export const ChallengeTC = composeWithMongoose(Challenge);

I have to also perform gql query to get the challenges details of the the user and also have to query all the users of a particular challenge.