Error loading my app

when I'm trying to run my app it writes:

E/AndroidRuntime: FATAL EXCEPTION: main
              Process: com.inbar.amit.ksharet, PID: 8466
              java.lang.RuntimeException: Unable to instantiate service com.inbar.amit.ksharet.MyFirebaseInstanceIDService: java.lang.ClassNotFoundException: Didn't find class "com.inbar.amit.ksharet.MyFirebaseInstanceIDService" on path: DexPathList[[zip file "/data/app/com.inbar.amit.ksharet-2/base.apk"],nativeLibraryDirectories=[/data/app/com.inbar.amit.ksharet-2/lib/x86, /system/lib, /vendor/lib]]
                  at android.app.ActivityThread.handleCreateService(ActivityThread.java:3147)
                  at android.app.ActivityThread.-wrap5(ActivityThread.java)
                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1550)
                  at android.os.Handler.dispatchMessage(Handler.java:102)
                  at android.os.Looper.loop(Looper.java:154)
                  at android.app.ActivityThread.main(ActivityThread.java:6077)
                  at java.lang.reflect.Method.invoke(Native Method)
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
               Caused by: java.lang.ClassNotFoundException: Didn't find class "com.inbar.amit.ksharet.MyFirebaseInstanceIDService" on path: DexPathList[[zip file "/data/app/com.inbar.amit.ksharet-2/base.apk"],nativeLibraryDirectories=[/data/app/com.inbar.amit.ksharet-2/lib/x86, /system/lib, /vendor/lib]]
                  at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
                  at java.lang.ClassLoader.loadClass(ClassLoader.java:380)
                  at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
                  at android.app.ActivityThread.handleCreateService(ActivityThread.java:3144)
                  at android.app.ActivityThread.-wrap5(ActivityThread.java) 
                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1550) 
                  at android.os.Handler.dispatchMessage(Handler.java:102) 
                  at android.os.Looper.loop(Looper.java:154) 
                  at android.app.ActivityThread.main(ActivityThread.java:6077) 
                  at java.lang.reflect.Method.invoke(Native Method) 
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865) 
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755) 

does some]one know how to fix it?
thx for all the answers.