Check the model description and its normal refill method. A removable reservoir filled by hand is different from a dispenser connected to the household water supply.
What the observation tells you
That distinction changes the useful first observations. An empty tank cannot be corrected by searching for a supply valve, and a plumbed system should not be dismantled as though it were a removable jug. The external dispenser appearance may not reveal the difference.
A useful next step
Read the manual and describe how water normally reaches the appliance. Do not pull out the fridge or disconnect pipework just to identify the system.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.