How do I utilize a lookup table?

[not_a_pro]

I have a lookup table of all customer office information. 

I am creating several lists where the user has to input their office ID when submitting a query. 

When I create the list, I am utilizing the 'choice' column; but is there a way to reference a datasheet (excel) that has the current customer office ID's? As an example, we add/deleted(archived) 20+ office ID's a year and I need the list selection to be dynamic to what is added. 

I see the option for 'Lookup' but it seems to only reference other libraries/lists and not actual data tables such as excel. 

[#2 · Accepted solution]

@not_a_pro 

"Lookup" columns in SharePoint can only reference data from other lists not other datasources.
But you can quite easily create a new list based on an Excel file 

Then you can create a lookup to that list.

But this works only once (when you create the list)... After that you will have to make updates on your office ids in that list, not in your excel file.

But you can always sync data from that list back into your Excel File.