The quick and short answer to this question is: You can not become a member of the TC.13 as an individual. The Technical Committees of IFIP are based on the selection of representatives from the national computer organisations.

However, if you wish take part in the work of the TC, you might join one of the six working groups who are actively working through conferences, workshops, task forces and other events to promote Human-Computer Interaction research and education.  In order to do so, go to the working group you are interested in, and contact the chair person or the secretary, and they can provide the information you need to activate yourself in the group. We are always looking for people who are interested in active participation.