TCGA -LIHC Isoform Expression Data

Question

[jain72744]

Hello,

I have downloaded both miRNA expression files and isoform quantification files in R for TCGA-LIHC. Now, I wish to extract all mature miRNAs from these which I found to be present in the latter isoform files and their respective raw counts. But I am unsure how to process this data further and get the arms as 3p or 5p. Kindly guide me regarding the same and provide any links, if available, for reference.