If you are planning to adding the Yubikeys as a hard token for your users in ESET Secure Authentication installation you'll most likely have ended up at the ESET guide on how to do it found here:
https://techcenter.eset.nl/nl/kb/articles/using-yubikeys-with-eset-secure-authentication

The problem with this guide is, it assumes you only use the Yubikey as a hard token for ESET and NOTHING else.
Like most people, I use these keys as 2FA for facebook for example.

If you followed the ESET guide word for word and overwritten your Configuration 1 slot. You basically lost the ability to generate OTP for any of your applications and you need to reconfigure your key.
I recommend you follow the Yubikey guide on how to do this: https://support.yubico.com/hc/en-us/articles/360013647680-Resetting-the-OTP-Applet-on-the-YubiKey

Yubikeys come with 2 configuration slots. In most cases the second one is always empty and you are free to configure this.
The reason for the 2 slots is that slot 1 is for short press and slot 2 is for long press. This way you can configure 2 different actions when touching the yubikey when inserted.
(Short press means you press the button and let go within 2.5 seconds and Long press means you hold the button for 3,5 seconds)

Therefore, when you want to configure your Yubikey as a hard token, instead of choosing slot 1 as the guide says, choose slot 2.
It is possible to swap the slots where OTP is slot 2 and ESET is slot 1. It all depends on what your preference is.