Python is a very commun programming language which can run server side.
Openpyxl is a library for python to read/write excel spreadsheets.
Sensor.Community uses an API to receive the data of all the sensors. This API is described here: EN APIs · opendata-stuttgart/meta Wiki · GitHub
You can write a porgramm which calls and loads the excel file. With openpyxl, you read the values and the time and prepare a json file compliant with the one which has to be sent to the API. You do a POST request with Python.
You will need a server or you’ll have to let a computer run…