Hi Maureen! If your shea butter is on the hard side, you might want to completely melt everything down first (the butter and oil together), then chill it in your fridge, then try whipping it.
It will be similar to the instructions in this article: https://thenerdyfarmwife.com/homemade-body-butter/
The arrowroot or cornstarch is totally optional – another thing that works in its place is tapioca starch, but if you don’t have any, that’s fine too.
I more often just adjust the oils so the body butter is light, and don’t often add the arrowroot, etc.