Sharepoint-Need to sum criteria from List 1 in List 2

[arussell9]

Hello,

I have two lists. List 1 has employee names, # of assignments, date of assignment, days since assignment. List 2 has employee names and number of assignments. 

I can't figure out how to create a flow that when an item is created in list 1 that list 2 updates the total # of assignments for the matching employee since x # of days. 

Any help is appreciated.