You may learn process design and simulation, some simulation softwares like Aspen, Chemcad, etc.
You may learn some CFD softwares like Ansys, Comsol, etc. Learn Matlab.
Attend workshops and short term courses on topics that interest you.

You can even look for internships in your area of interest. Doing these will not only enhance your resume but also increase your knowledge and skills.
All the best!!