Please note, not all scheduling options will be available when editing an existing med such as custom intervals. You can re-add the medication in order to get all of the options.
Android
If you are trying to change the schedule and do not see the option you need, you will need to turn off the reminders and turn them back on.
Tap 'Medications'
Tap your medication then tap the pencil icon
Toggle OFF 'Reminder times, then tap 'Done' to save
Tap the pencil icon again
Toggle ON 'Reminder times'
Tap on "Schedule" and select your desired option.
Set the reminder times according to your new schedule.
When you are finished, tap 'Done' to save
iOS
Tap on 'Medications'
Tap on your med and tap 'Edit' on the top right corner
Tap on 'Reminders' then tap on 'Frequency' and select your new schedule and set the new times for your doses