I'm amusing that you have RDD[String]
and you want to extract both columns from your data. First you can split the line at length 7 and then again at 4. You will get your columns separated. Below is the code for same.
//creating a sample RDD from the given string
val rdd = sc.parallelize(Seq("""2107abc2018abn2019gfh"""))
//Now first split at length 7 then again split at length 4 and create dataframe
val res = rdd.flatMap(_.grouped(7).map(x=>x.grouped(4).toSeq)).map(x=> (x(0),x(1)))
//print the rdd
res.foreach(println)
//output
//(2107,abc)
//(2018,abn)
//(2019,gfh)
If you want you can also convert your RDD to dataframe for further processing.
//convert to DF
val df = res.toDF("col1","col2")
//print the dataframe
df.show
//+----+----+
//|col1|col2|
//+----+----+
//|2107| abc|
//|2018| abn|
//|2019| gfh|
//+----+----+