Just separate the numbers by a comma, no spaces.
For example let's say you want to run GPU0 at 950, GPU1 at 950, GPU2 at 900, and GPU3 at 950 you would enter 950,950,900,950 in the Core MHz field. Same goes for the Memory.
I have tried this but then Core/Mem clocks shows just 300 300 300 950 (0) and 300 300 300 1500. Should this work also in this R edition smos?
I haven't used the R series, but with the rx series you can usually fix that by changing the clock speeds up or down a bit. I would try changing them to 925 or 975 and 1475 or 1525. Basically just play around with the numbers until you find some that work.