DW bought a new cell-phone. I helped her set it up but she wanted a secure lock. We drove to the Verizon store where a man helped her setup the passkey with her fingerprint, with a security code for backup. Her fingerprint worked at the Verizon store but has never worked since.
I called the Verizon store and asked how to erase the fingerprint unlock. The guy said every Verizon store employee has the code to bypass the fingerprint and security code requirement to unlock a Verizon phone.
How secure is that?
I doubt that what he told you is true. You didn't state whether the new phone was Android or IOS, and I have zero experience with IOS (Apple phones), but I doubt that they are less secure than Android.
So, if the phone is an Android, it's pretty straight forward to get into the settings on the phone and change the fingerprint to a different finger or delete it entirely. The same is true with the security code "backup".
First, unlock the phone with either the fingerprint or the security code so that the phone is open and ready to use. Then, go to settings and scroll down to "Security and Privacy" and tap that. When the Security and Privacy page opens, scroll down to "Device Unlock"....and tap that. You will now see a page that has "Screen Lock (PIN)" and the other section that is called "Fingerprint & Face Unlock." At that point, you can change either one of them or both......the PIN....and/or the Fingerprint & Face Unlock.
If you want to change the PIN, you will have to enter the existing PIN, in order to access the area for changing it. Once you do that, your options are None, Swipe, Pattern, PIN, or Password. Once you've finished there by selecting something different or keeping what you have, you will have to confirm any changes made and then it should go back to the "Device Unlock" page.
Once the device unlock page is open, you can now select the "Fingerprint & Face Unlock" section to change or delete the existing fingerprint section. There is also a method to use facial recognition (I use fingerprint myself), so I've never tried that or used that. So tapping on the fingerprint section will open a page that shows the existing fingerprint or fingerprint(s) that are in use and they can be deleted individually if there is more than one (which is always a good idea to have more than one......think about an injury to that hand/finger and not usable for a while). There is also a + sign to add another fingerprint. At this point in time, I would make sure that the PIN number that she uses works correctly and as expected, then go in to the fingerprint section and DELETE it (or delete all fingerprints if there is more than one) This procedure is basically starting over on the fingerprint sign in method. Have her wash her hands with soap and water to remove any oils/dirt/grime/whatever, and then go through the fingerprint setup again, until you get one that actually works.
And last but not least, some Android phones will have a setting that can be turned on that will make the fingerprint sensor more "sensitive" IF you are using a screen protector on the phone display. If she isn't using a screen protector, you might still want to experiment with this setting. So again, go to Settings, then scroll down to "Display", then scroll down until you see "Screen Protector Mode". When you find that (if your phone has it), toggle the slider to ON and the touch screen of the phone will be more sensitive to not only the screen itself, but also for the fingerprint reader part of it. Having said all that, not all fingerprint sensors are on the phone screen and they have their own separate sensor somewhere on the body of the phone. I've had a couple of phones like that, but my current phone, a Google Pixel 7, the fingerprint reader is on the phone screen itself.