Igst instead of cgst and sgst

I paid IGST instead of cgst and sgst and filled gstr3b but correctly filled gstr1 and also paid cgst and sgst while filling next month gstr3b. Since I paid GST twice on a particular goods first wrongly IGST and then cgst and sgst what are the remedies available out of the following

1) since in coming months I have output IGST liability can I file gstr3b without paying tax since I have already paid IGST in preceeding month wrongly.

2) if refund is the only option then how to file refund application since on GST portal there is no option of refund in case of wrongly paid GST.