I don't see any dataset collections in your account that are the results from the tool "Stringtie". There are only individual runs/result files. These won't show up in any of the collection operations tools as valid inputs.
How to use collections: https://galaxyproject.org/learn/
- Start here: Dataset collections - modern studies usually include many samples. Collection are designed to simplify complex, multi-sample analyses as shown in this tutorial. https://galaxyproject.org/tutorials/collections
- Advanced functions: http://galaxyproject.github.io/training-material/topics/galaxy-data-manipulation/
Hope that helps. If you need more advice, please explain what you are trying to do and include exact tool names for functions. Leave any associated input/output data undeleted in your history otherwise our help will be limited. If you want to, the actual datasets involved can be named by number along with the history name (you don't need to share a public history link in a post here if working at https://usegalaxy.org). If you'd rather keep it all private, the same information can be sent to firstname.lastname@example.org from your registered account email address (internal support list for Galaxy Main).
Thanks! Jen, Galaxy