This is most likely a design issue.
You need to modify the process you use (open Console ->Administration -> Process Designer) - that is where all the actions are defined.
You will need to add the action "add notification" when status changes to "with customer" or "with 3rd party".
Insert an automatic action (green box) to the process between the “With 3rd Party” (blue box = manual action) and “Stop Clock” (green box) and link to the “Add Reminder” action when prompted. Now link up transition lines so that it is inserted between the two original blocks. Now drill into the “Add Reminder” block to set its contents. Tip: you see other reminders in you screenshot so take the lead from these examples by drilling in and reviewing how setup.
Happy to help further if needed once you get stuck in.
As always and especially as you are new to this then I recommend you play in a DEV instance wherever possible, especially as the process needs to be offline to make any changes.