What you’re looking for is functionality similar to the PlaceInBottom that we had in classic NAV reports. But that’s not really possible out-of-the-box with Visual Studio and RDLC.
There are a few things you can do instead, which is described in this blog post:
Once i got this sort of requirement, I believe what I did was I did the totalling in Body itself and then used the reference in Footer.
Just the same concept as of GetData SetData.