Hi @Micka_Rakotomalala, I am very sorry to hear you’re having trouble 
The date format you are seeing (values such as 44562 or 44047) are no actual errors, but instead are how Excel stores dates. n8n does not have built-in functionality to automatically convert these, but you can use a Set node with a bit of Excel specific logic to process these. Check out Date serial number to normal date - #4 by MutedJam for details and please do let me know if you are still running into any trouble with this 