you can reset it by deleting the existing keyring and creating a new one.

Important: This will remove passwords and other credentials stored in that keyring. You'll need to save those again when applications request them. It won't change your Kubuntu login password.​

install seahorse if it is not already installed
Open Passwords and Keys from the application menu.
In the left-hand panel, look under Passwords for the keyring named Default or Login.
Right-click the relevant keyring and select Delete.
Confirm the deletion.
Log out of Kubuntu and log back in.
A new keyring should be created. When prompted, set a new password. I'd recommend using your normal Kubuntu login password so that it can unlock automatically when you log in.

PS:If you set the new keyring password to match your Kubuntu login password, the keyring should normally unlock automatically at login (provided automatic login isn't enabled).
That should get Proton VPN working without repeatedly asking for the forgotten password.
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