Trying to change active user based on dates

Hello,

I have a SharePoint list with several fields:

• Person A 
• Person B
• Active Person
• Start Date
• End Date

I want to set up a flow so that when a list item is modified, a flow checks if TODAY is between Start Date and End Date. 

If true, [Active Person] = Person B

Else, Active Person = Person A

Any idea how I can do this?