If you have rJava installed already, try this, for example,
Needs["RLink`"]
JLink`UninstallJava[]
InstallR["RHomeLocation" ->
"C:\\Data-Work\\Programs\\R-3.5.1\\App\\R-Portable",
"NativeLibLocation" ->
"C:\\Data-Work\\Programs\\R-3.5.1\\App\\R-Portable\\library\\rJava\\\
jri\\x64"]
REvaluate["R.Version()"]
I'm using Window 10 (1803) and Mathematica 11.3.
"RHomeLocation" - path to your R and "NativeLibLocation" - path to Java R Interface
see this for more details