GST refund FY 2017-18

Refund for what?

Refund of Excess credit due to rate variation between inward & outward supply

You can apply even before filing of Annual return also.
section 54 is applicable in this case.
If tax rate of your outward supply is lesser than your Input supply, you can claim refund of Input Tax.

in this case you can claim refund only on rate difference on input.
and not on input service or capital goods.

Can you specify the goods you are dealings.... as refund under Inverted duty structure on few goods was block in few goods.
Kindly refer Notification 5/2017 CT (R) : specify the goods on which Refund cannot be claimed Under Inverted Duty Structure.
And Refer Notification 20/2018 CT (r) : Amending Notification 5/2017 CT(R) allowing refund claim on IDS

Manufacturing of Knitted Cloth from yarn

Well in that case... as I know input tax on yarn is 5% and output tax rate on job work is also 5%
hence you can not claim refund.

Input of Yarn is 18%, which was reduced to 12% later

Many categories of yarn come under 5%, hence check it as per specified HSN.

and if your yarn input is at 12% and fabric output is 5% then you are eligible for refund.

kindly note- You can not claim refund related to input service and capital goods.