That's a very good question @Alzahrani, don't even know if that is possible anymore, maybe you would need to cancel the premiere edition or pro subscription you already have to activate the founder's one, but just to be sure I would recommend you to ask Stadia support in this case what to do.
I contacted Stadia support via Twitter and they guided me to delete the service from my account as an option to solve the issue. After I deleted Stadia data from my account, I found out that I need to wait 30 days for the deletion process
. I am not happy at all. I had to purchase the hardware twice, then I had to delete my pro subscription (3 months of subscription is lost) and now I have to wait 30 days to activate my founder edition code. I won't be surprised that my founder edition code will be expired by that time. unbelievable
.