How to use automations/scripts to add numbers in one field to total in another field

Hello, I’m not a developer, but I’m trying to work on an automation using scripts that will take the inputed “Current Monthly Image/File count” number and add it the “2021 Image count” total for every record in my table. Every month someone else inputs the number of images captured by a photographer in “Current Monthly Image/File count” and I want to add that number to the annual image count in the “2021 Image count” field.

Thanks!