The GVL has a good assembly tutorial. Please see: https://www.genome.edu.au/learn/
You might also review the IMG new guidelines and/or contact them for suggestions so that the output you end up with is what their tools are expecting as input.
Assembly tools already wrapped for Galaxy can be found in the Tool Shed. Many are for use in a local or cloud Galaxy. If your target tool(s) are not wrapped yet, in all likelihood they could be.
Thanks, Jen, Galaxy team