Since the transition from Trinket this has become much more difficult. If you are using a paid-for plan with GoCodeIt or Dodona then the facility to set assignments and save work is built in. If not, students will need to copy and paste their work into another application to save it.
Saving:
Loading:
This is not ideal, but students soon get the hang of it if they do it often enough.
Alternatively you could use GoCodeIt as the source for the challenge and boilerplate code and then code it in an offline IDE such as IDLE or Thonny.
We are considering better alternatives.