Hi @Xolex Nguyen ,
here you can see how the reserved instances are applied if there is a resizing in the same VM series (same instance size flexibility group):
https://learn.microsoft.com/en-us/azure/virtual-machines/reserved-vm-instance-size-flexibility#examples
----------
(If the reply was helpful please don't forget to upvote and/or accept as answer, thank you)
Regards
Andreas Baumgarten