Hi,

I think you can use this security :

In flow action level we can define security with privilege will solve the problem

Hi 

U can solve this by using AccessManager landing page  in pega.

DesignerStudio>> Org&Security>>AccessManager

Hi

We can not use local action on assignment in screen flow, but we can use local action in screen flow rule. Please find attachment (Screenflow_localaction.png)

Path: Flow rule (Screen flow) --> Design Tab --> Select Local Action

Open local action rule (flow action rule) --> Security Tab --> Select When rule in Required condition field. Please find attachment (Localaction_WhenCondition.png)

Path: Local Action rule --> Security Tab --> Require Conditions

In the when rule use below conditions 

1. pyWorkPage.pxStageHistory(<LAST>).pxProcesses(<LAST>).pxProcessName = 'your flow name'
2. @Utilities.LengthOfPageList(pyWorkPage.pxFlow('your flow name').pyFlowPath)="Assignment number" (Example: 1 or 2 or 3 or etc)

Let say, we have 5 assignments in the screen flow, and you want to display this local action 1st and 3rd assignment then use 1 and 3 in the Assignment number place in the above 2nd condition.

I think this may help for your requirement.

Thanks