How to convert install type index for SetSectionInInstType use

let's say

GetCurInstType $R1

.......

!insertmacro SetSectionInInstType ${blah} ${INSTTYPE_X} 

In the next step, how to change $R1 to ${INSTTYPE_X}?

It already contains the index of the installation type. You can't convert it to the original define, because that only has meaning in the context of makensis.