Grip shifters are designed to fit on bars that are 22.2mm OD; most drop bars are 25.4mm or 26mm OD - thus they will not fit.

The easiest solution is bar end shifters, which are available in both friction and index. For example:
https://www.amazon.com/MicroShift-Do...ifters+9+speed

There are solutions keeping the grip shifters, but they are heavier, more complicated and require custom fabrication.