Macro to scan multiple columns and find total sum of each unique item on a list of unique

Good day. Been struggling with this and would appreciate some help. I'd like to write a macro that goes through multiple columns in a sheet and sums the total values of each item beside it's cell in a unique list. Similar to how to find for eg. sum of total sales for multiple months for a particular product. I have attached a sample sheet to explain. The update sheets are to show how the input data worksheet would expand over time, so the code would need to work for a dynamic range. So far working on it i've found i might need a SUMIF INDEX-MATCH array function, but i don't know how to write it. I use Excel 2013.



Would be grateful for any help