A Regulator is a 3 pin chip which so long as you supply it with a voltage above say 5.7 V will supply a nominal 5V. ALL modern RC rx have these built in (as do some servos)as a lot of airborne sets are used with dry cells (yes still) and 4 x fresh new dry cells will give 7V or maybe a bit more.

Don't worry about it, you wont burn out a servo unless your control runs are tight otr the servo is wrong for the application. Check your batteries after a couple of flights or use a battery monitor.

6V is good!