Essential: In Project64, click on "Options" and then on "Settings" in the "Options" tab, uncheck the box "Hide advanced settings".
Then it is necessary to return in the settings, there there will be much more tab, click on "Settings of the rom", and put the size of the RDRAM to 8mo.

https://www.romhacking.net/hacks/8640/

Read Me (English):
https://s3-external-1.amazonaws.com/romhacking-hacks/hacks/n64/patches/8640readme.txt