Here is the way to adjust the belt, the printer is using the adaptive adjustment of belt tensioner. There's four secure screw on the back side of each belt tensioner. Please loosen all the 8 secure screws and follow the video below to adjust the belt tension automatically by moving the print head ( please move the printer head in the direction shown in the video , after adjust it, please tighten the screw back )Please see the photo and video in the link below.
1.Please loosen all the 8 secure screws.
2.Belt Adjustment
Belt Adjustmeng Video