How can I update the ota after I unroot on my Lenovo a6000 plus?

[Vinaykumar436]

I have lenovo a6000 plus
I was rooted my phone using kingroot then I unrooted my phone to get ota update .
When i installing update after few seconds It shows error in installing a update.
I tried so many times but isn't working. I frustrated by this . please help me is there any solution for this please help.....