Forgot alternative password for encrypted & fingerprint-protected Samsung Galaxy S5: how to reset it?

Question

So I have an encrypted Samsung Galaxy S5 with Android 6.0 and set fingerprints for its lockscreen (fingerprint is set as lockscreen-type for the setting device encryption). Now it seems like I forgot my alternative password - or at least what I tried didn't work.

I can still unencrypt my phone with my password and unlock it with my fingerprints. I didn't need the alternative password so far.
But I'm not sure if it's possible that this could change - e.g. if I happen to make too many false fingerprint-attempts(?) What would you recommend me to do?

I'd prefer changing / resetting the alternative password only if that's possible.
This page has some info which could be relevant here. However that's not for encrypted phones plus I'd like to make sure that I'm not breaking anything.

Answer 1

Okay so it basically solved itself by now: I tried to enter the passphrase many times. Then I used my phone as always and then I shut down. After reboot it showed a screen with an option to change the alternative password. Great!

^{I think I might have failed to enter the passphrase correctly because it only accepts 16 characters and iirc the password I had was longer than that. Actually what I thought was my alternative password was shorter than 16 characters.}

Follow-up question: "Alternative password has been set as the decryption password"

Another follow-up: now the data on my encrypted SD card has been wiped. Not sure why this was done - the apps still work but the photos on it are just unreadable files. Great.