iPhone X

That is not something that you set. That is controlled by your wireless carrier. Some carriers have the ability to modify it slightly, but not much. It isn't based on the number of rings, it is based on time, and while a carrier may have the ability to adjust, it may only be a second or two.

Contact your cellular carrier customer service. That is an option they control. Some carriers have limited options to change the time before a call goes to voicemail.

You're welcome.

Ha! I do what I can. Enjoy your iPhone.