What belongs in your text
Add two to four short points for each job. Explain your work, not only your title. For training assistant, this matters when you explain exercises and plan sessions. Write what you did, where it happened and why the work was useful.
A good example is a short account of how you check progress and answer questions. It shows real work rather than an empty claim. If you have not done that task, choose a different example from your own work.