Welcome, @angel
Tools screen for specific datatypes when accepting inputs. For this input, the tool is expecting a dataset with the tabular datatype assigned.
How to know which datatype a tool is expecting is in this topic and a few others.
Search: Search results for 'tool doesn't recognize input' - Galaxy Community Help
Situations when the (unavailable) message can be generated
- Dataset 72 was originally accepted by a tool run.
- It had a tabular datatype assigned, or was drag-and-dropped.
- The latter breaks some built-in checks – you can try this way but expect problems exactly like this.
- Or, the first was done, but the datatype assigned to dataset 72 was modified to be something other than tabular.
→ When the “rerun” function is used to load up the tool form, it preloads what was originally input. If the metadata datatype was changed to be anything other than tabular, it won’t be accepted.
Keep in mind that none of this is about the file content. The data still needs to be in tabular format and have data in the columns it can understand.
Examples are down in the help section of the tool form. The GTN also has tutorials.
https://training.galaxyproject.org/training-material/search?query=MAGeCK
There is a training event going on all week if interested. It is not too late to join. The bonus is a dedicated chat per tutorial, and the authors and other Galaxy scientists are there to help (including me). Smörgåsbord 3: A week of Free, Online, Galaxy Training supported by the Global Galaxy Training Community
Hope that helps! 
