Is there way to fix a disc brake rotor if slightly bent? Rear disc on my Acid 2016 is little bit bent so while riding it makes a strange noise when that part of disc comes through the caliper. Is there any way fix that or should I buy new disc?
Yes. Disc brake rotors can warp a little in use, or get bent from impacts and straightening them is routine maintenance.

The basic procedure is to find spots where the rotor is bent inboard or outboard, and carefully incrementally bend it back. There are tools made for this purpose (e.g. Park tool DT-2) but the job can be done with a large adjustable wrench.

There are many tutorial and how-to videos that show you how to perform the procedure. Here's one from Park Tool.