For mapping coordinates to genes (any data), this prior Q&A covers how-to: https://biostar.usegalaxy.org/p/11833/
For Cufflinks/Cuffmerge/Cuffdiff data:
If the reference annotation (GTF) supplied to Cufflinks already contains the gene_name attribute, you can use the tool Cut to isolate the value.
If the GTF used didn't have this attribute, consider using a GTF that does have it (iGenomes is one choice). Details are in a prior Q&A post (and those linked from it): https://biostar.usegalaxy.org/p/19615/
Many more posts about this are in other prior Q&A and can be reviewed/search for in the sidebar of similar posts >>>
AND if you would rather avoid all of this extra processing - and use improved RNA-seq analysis methods - you could switch to using the latest tools. See the Galaxy tutorials here for example workflows: https://galaxyproject.org/learn/
Thanks! Jen, Galaxy team