As a Seller, if you’re only seeing the option to “Assign” an Easel Assessment or Activity that you’ve created, it is likely because you created it “For my classroom” as opposed to “For my store” (see image below).
If you accidentally create an Easel Assessment or Activity in the “For my classroom” section, you can resolve the issue by clicking on the three dots to the right of the “Last Edited” date, then selecting the “Add to TPT Listing” option (see image below).