It is not possible to load only one transcript from the default annotation track that is automatically loaded with the reference genome.
You can however load a separate file that only has the transcript you are interested in. To create that file, you could for example download the same RefSeq annotation file that IGV uses, and then extract just the transcript(s) of interest into a separate file and load it into IGV via File > Load from File. Mousing over the RefSeq track name in IGV will show you exactly where to find the file, including the full URL.