DAX - New or Existing User

We have a table of actions for users that includes a PersonID and an ActionDate

1. We need to identify whether users are NEW USER or EXISTING USER when we use month/date/year slicers (there is a Date Dimension)

2. We created a NewUserFlag to highlight first action to define NEW USER or EXISTING USER

3. If we were to filter calendar year to 2019 the report would need to show that PersonID = 101 was a NEW USER in that period, but pull back both actions (i.e. Key 1 & 4)

I'm guessing we need something that sees where NewUserFlag is both NEW USER and EXISTING USER in selected period and allocate all associated actions to a NEW USER

Key   PersonID     ActionDate    NewUserFlag

1       101              01/01/2019    NEW USER

2       102              03/05/2019    NEW USER

3       103              03/06/2019    NEW USER

4       101              01/05/2019    EXISTING USER

Any help appreciated!

dombot5000