we are getting the below error
we can customize the trigger exception and can made this error to user friendly ?
system execution of afterinsert caused by system.dmlexception update failed first exception on row 0 first error field custom validation  exception issue

please help?

I had one trailhead account but it had email address of my previous organization. I had linked that trailhead account with webassessor.
I have created new trailhead account with my personal email address now. And merged the old trailhead account in new one.
So all badges and points are visible in new tarilhead account.
But webassessor is still linked to the old trailhead account only. So whichever maintenance exam I am completing is not reflecting in the results.
I tried to link the new(merged) trailhead account with webassessor but I am not getting any unique verification code on my email. So I am not able to link it.
Can anyone help me to link this new account and remove the old link?

I am unable to make an existing app visible in lightning experience.  Most of my apps are visiable but a few are not.  They are not console apps.  I am not able to check the checkbox to make them visible.  I hope someone can help me.  Thank you.

we are getting the below error
we can customize the trigger exception and can made this error to user friendly ?
system execution of afterinsert caused by system.dmlexception update failed first exception on row 0 first error field custom validation  exception issue

please help?