There is a mongo spark connector maven package.

org.mongodb.spark:mongo-spark-connector_2.12:10.1.1(link: https://mvnrepository.com/artifact/org.mongodb.spark/mongo-spark-connector_2.12/10.1.1)

spark.conf.set("spark.mongodb.write.connection.uri", "mongodb://<username>:<password>@<host>:<port>/<database>")
spark.conf.set("spark.mongodb.write.database", "your_database")
spark.conf.set("spark.mongodb.write.collection", "your_collection")

##read table
delta_df = spark.table("your_database.your_table")

##write to mongo.
delta_df.write \
    .format("mongodb") \
    .mode("append") \
    .save()