Hi!
You can try to run the following command in the Skype for Business PowerShell.
Set-CsClientPolicy -EnableVOIPCallDefault true
To be noticed that this policy setting only affects the initial state of the click-to-call feature. If the user modifies the value of the click-to-call setting then the user-selected value will override this policy setting. After a user has modified the click-to-call setting that setting will remain in use and will not be affected by the EnableVOIPCallDefault policy.
For more details, you can learn it from:
https://learn.microsoft.com/en-us/powershell/module/skype/Set-CsClientPolicy?redirectedfrom=MSDN&view=skype-ps