Add a dataview on the page having as datasource the Teacher. (sidenote: keep entitynames singular, so Teacher, without ‘s’)
in that dataview add a datagrid having as datasource the TrainingEvents over association to the Teacher.
How can i now add an existing Training event for that teacher from the same screen
you need to add some logic here..
You have to display a listview/datagrid of the TrainingEvents (that are not already affected to the Teacher)
and add a button 'Affect to this teacher'
and in the microflow you just change the object TrainingEvent and fill the association with the teacher (parameter object of your page)
let me know if it’s not clear :)