I have 800 miRNA but about 20 up and 20 down regulated more than 2 fold change between the control and treatment group. I need to perform heat map but don't know which columns to import and whites the code to use.
I would do a subset of the complete matrix by selecting only the genes with significant differential gene expression. After that use the filtered matrix to do the heatmap with R. Here, you can find a short tutorial for heatmaps in R: https://sebastianraschka.com/Articles/heatmaps_in_r.html
If you don't have much experience with R, you can try the following online tool, where you have to upload your data of interest for the heatmap: www.heatmapper.ca/expression/