Welcome @Akriti_Tewari_Res_Sc
The GRCh38/hg38 genome is available in RNA STARSolo at UseGalaxy.org, UseGalaxy.eu, and UseGalaxy.org.au.
If you are working at a different server, you will need to make the request to the administrators of the server directly. The contact information is usually on the homepage or login view of the server, but let us know if you cannot find it and we can try to help more here. We’ll need the full URL of the website (find this in your browser window at the top!).
If this is your own server, then you can either load the genome directly (with the Data Managers), or attach the shared CVMFS resource (much easier!). Search the Admin Training area with “cvmfs” to find those tutorials. → Public Galaxy Servers
Or, you can move your work over to one of the UseGalaxy servers, run this step, then download or move your data back (by URL if a hosted server, by download/upload for the others). → FAQ: Transfer entire histories from one Galaxy server to another
Hopefully this helps but please let us know if it actually does! 