Hey @Anonymous,
Exactly as @PrasadAthalye said you need to follow his flow design.
The first step you will need to complete if you haven't already is turn your excel spreadsheet into a table, this will allow flow to read the information inside of that table. To do this just highlight your chosen area in excel and go to the insert tab and insert a table.

On the flow use a reoccurrence trigger and set it to trigger 1 weekly and in advance options you can define a day and time for the flow to trigger.
Additionally, add the List rows present in a table action, and put flow to your files location within SharePoint.

Get the SharePoint list where the students uploaded their assignments to and filter to see which students have uploaded their assignment and which ones have not. The filter query should look something similar to this; Title eq 'Student Names'. Where title is the column name in your SharePoint list and Student Names is your column name in your excel spreadsheet. Student names should be dynamic content from the excel action.
Using a condition we can filter to see if the student has uploaded their file to SharePoint or not. If the value returned from Get Items is greater than 0 it means there is an item assigned to that student and therefore no action is required. If the value is 0 then no item is assigned so send an email to that student to remind them to upload there assignment. The formula is;
length(outputs('Get_items')?['body/value'])


The Send an Email actions, email is from excel and any content from excel can be added to the email.
Cheers
Campbell
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