I can't change nickname

! Please help solve one question. I am a mail administrator on the corporate domain elektrosvit.com.ua. After changing the address of the mailbox of one of the users vasyl.yavorskyi to the address o.sklyar@elektrosvit.com.ua, the old nickname is still saved and does not change in the application to android and iOS

Now it looks like this:

vasyl.yavorsky

o.sklyar@elektrosvit.com.ua above the old nickname, and below the new address Please help solve this problem, I can't find the settings to change it