You will need to call Dell support and provide the requested verification of ownership.  If the system is out of warranty, there is a standard support call charge for the issue.

Thx for your answer. I'll have to provide requested verification of ownership on the phone ? Huw does that work ?

You will need to provide the address and phone number (likely with email address) of the current, registered owner of the system. 

@ejn63​ you mean the address & phone number registered on my Dell acount on which I registered the computer too ?

Yes.  if you are the registered owner, you will just need to confirm that with the technician before they'll assist you in unlocking the system.

Thanks a lot, I will do it next week ! 🙏

I hava a problem : my account sets an address in France but Dell "detects" that the computer is in Finland & only offers service whether in FInland or international. How can I set the computer in France rather than, Finland ? Because the computer isn't in Finland, me neither & I don't speak Finnish

If you purchased the system second-hand or through a retailer, you will need the assistance of the seller to rectify that.  It really should not matter where the system is, as long as you have the owner's details (you can't obtain free support -- for this issue you will need to contact paid technical support).

@ejn63​ Thx for the answer, so the name of the cie that sold me the computer correct ? Can I call the french customer support or do I have to go through the Finnish one as the website suggests ? (I don't understand why the finnish one though as I bought it from a Polish cie)

They will need the ownership records from whoever (or whichever company) -- presumably in Finland -- is the current registered owner of the system.  If you can't provide those, Dell will not unlock the system.  At that point, if this was a used purchase, return it to the seller for a refund.  Otherwise, you'll be adding the cost of a replacement system board to the purchase price.