Hi @Houssem-Eddine0,
Yes, "if necessary". If you request to change to a different room and the host accepts, you will be changed to that room. However, some hosts charge more/less for a different room (maybe it has a bigger/smaller bed or has an ensuite bathroom") and therefore maybe an extra amount or refund would be applied. Maybe it is a straight switch and an extra charge or refund is not necessary.
I think the wording is as clear as they could make it.
Here is how to contact Airbnb if my answer does not satisfy you: Contact Airbnb
I hope I have helped you @Houssem-Eddine0
Also, is Eddine your last name? If so, you might want to remove it as it could open you up to scammers.
Dave
David
Superhost Ambassador ~ Host Club Community Leader ~ Experienced Co-Host