Reverse charge

Yes , once u claim it as input in ur returns then u can carry forward it

What if we are not having any output liability ?

- No more problem if no output liability. You can show the same in the same months in GSTR 3B return. Column 3.1(d) as outward & column 4(A)(3) as input... And pay cash payment as per value...

will rcm input will be carried forward to next month?
- Yes... it's C/f as regular ITC in Your next (& subsequent) GSTR 3B return...