If you are pursuing degree program in fashion designing then as a complimentary  courses you can opt for diploma or certification as per your interest and potential few of them I am mentioning below -

Diploma in Fashion and Apparel Design

Technical Illustration, both by hand and in Adobe Illustrator

Product Development

Diploma in Textile (Fabric and Trim sourcing)

Construction Courses (sewing, patternmaking, draping) etc.

Good Luck!!!