GSTR 3B, Table 4 - (2) Import of service

In my opinion, you should correct the same in the next month's return by doing the following:-

1) Enter the amount of RCM on Import of Services in Row 2.
2) Reverse the amount of ITC already taken in previous return, by declaring in Table 4(B)(2) i.e. ITC Reversed - Others, in next month's return.

Thanks

Can be rectified in annual return .

Yes you can correct the same in Annual Return. But, figures in Annual Return get auto populated. And if you will change the same and the difference between the figures auto populated and the revised figures is greater than 20% than, those fields will be highlighted in Red Colour and in the consequence Notice xan be issued to you for the same. Further if you will reverse the ITC wrongly taken in Annual Return then it will led you to pay higher amount of Interest on such reversal.