Okay - you want your rule on the control that changes, not the target field. Remove the rule you have on QUALITIFCATION-dataentry - you don't want the field resetting itself.
Based on your conditions, you need the same rule on three fields:
APP_SECTOR
APP_LEVEL
APP_TYPE
Rules fire when the field the rule is on changes. So, right now, your rule is only on APP_SECTOR. If you set it to "health" but APP_LEVEL and APP_TYPE are blank, your rule won't fire because the conditions won't be met. That's why you'll need the same rule on all three of those fields so that QUALITIFCATION-dataentry is set correctly when any of them change. You'll probably want to first add an action to clear the field as well - so that if the APP_LEVEL changes from 2 to 1 you don't leave the previous value in QUALITIFCATION-dataentry. Hope that makes sense!