If you're comfortable using NVflash (if not, I can link you to a guide, it is VERY easy to use), you can just flash the proper BIOSes on to the card yourself.
 
OC switch position BIOS: https://www.techpowerup.com/vgabios/227016/evga-rtx3090-24576-201110-1 
LN2 Switch position BIOS (520W Power Limit): https://www.techpowerup.com/vgabios/227017/evga-rtx3090-24576-201110 
 
personally, I would recommend running the 520W BIOS - contrary to what it's called, it does not natively disable any sort of protections on the card or anything like that, that has to be done with Classified Tool (disabling OCP etc), so it's not actually "dangerous" to use the 520W BIOS, as long as you're not messing with Classified Tool, there's no real chance of damaging your card, and it does not void your warranty.
 
Make sure you get NVflash from a reliable source as there is malware out there posing as stuff that's as popular as it is.
 
Basically, once you get the program, you load Command Prompt as Admin, go to the nvflash folder (make sure you put the BIOS files in that folder, also make sure you LABEL them as otherwise they'll have the same name... I did "GA102-520W" for the LN2 520W BIOS so I could tell them apart), put in "nvflash -6 BIOSNAME.rom" without the quotes and with the particular BIOS name where it belongs.   It will confirm the BIOS BELONGS on the card, if it gives you an error there something is wrong, then it will ask you to confirm you want to flash, you flash & then reboot.
 
Note, you can boot up on the Normal BIOS switch position, once in OS, switch to the OC position, flash the OC BIOS, then switch to the LN2 BIOS switch position & put the 520W BIOS on it, then reboot and you're good to go.