Unable to log in to Sandbox after passkey prompt – How can I recover Sandbox access?

I have one Production/Enterprise org connected to two Sandboxes:

• DEV Sandbox
• UAT Sandbox

Both Sandboxes were recently created, and I haven't logged into either Sandbox from any device yet.

When I try to log in to either Sandbox using my Sandbox username and password, Salesforce asks me to authenticate using a passkey.

Initially, I had a passkey saved in Microsoft Edge, but I removed it while troubleshooting. Now, when I try to log in, Salesforce gives me the option:

“iPhone, iPad, or Android device”

which displays a QR code.

When I scan the QR code using my iPhone, my phone opens Google Password Manager and shows:

I am still able to log in successfully to my Production org, and I am a System Administrator there.

My question is:

Since I still have access to the Production org but cannot log in to either Sandbox, is there any way to recover/reset the Sandbox passkey or generate a temporary verification code so that I can regain access to the Sandboxes?

I don't want to delete or recreate the Sandboxes. I just want to recover access to the existing DEV and UAT Sandboxes.

Any guidance on the correct Salesforce-supported recovery process would be greatly appreciated.