In this post I'll be going over how to maximize flight credits. It's essentially very similar to the process that you go through to find flights on Google flights, but in this case, it's important to select the carrier associated with the credit, which can be a bit tricky for the "everywhere" view since it only gives you options to select by 3 alliances, with no specific carrier names, & is even trickier if going beyond the main 3 US carriers.
Delta Example from SE VA for $200 Flight Credit on a Desktop or laptop:
Start Out on Google Flights with Unusually Flexible Paramaters
Narrow by the Carrier Where You Have the Credit for Alaskan Air, American Airlines, Delta, United, or Anther Carrier within 1 of the Main 3 Alliances.
Narrow by the Carrier Where You Have the Credit on Non-Alliance Airline
Option to Select Time Range
Option to Select Specific Dates
Select Amount
Move Around the Map Due to a System Bug