Payment of gst under rcm

i want to pay IGST under rcm.

I have GTA invoice. ( transporter from other state)

i want to pay IGST under rcm, i logged in to gst portal. i clicked the link of pay tax. 

and i came at the page where i need to fill amount of tax to be paid but there is no option that to be selected that its under rcm or not.

how to pay igst under rcm. please guide.