Hello Rob,
Thank you for your guidance and time. I followed your suggestion by reading Rocky's manual and found that on page 71, they indicated the UDMs in Fluent resulting from two-way coupled simulations. (Ref, ESSS Rocky, Release 2022 R2, CFD Coupling Technical Manual,
ESSS Rocky DEM, S.R.L., (2022).)

Then, I defined the number of UDMs location for 14 in Fluent.

In Rocky, I found that 14 UDMs I created in Fluent were available in the variable “from Fluent to Rocky”, not “from Rocky to Fluent”. 

I am curious, why did the UDMs I created in Fluent not be available in "From Rocky to Fluent"? (That is the reason why I think that I should create UDMs in Rocky not in Fluent, but I did not find the way to do it.)

Could you please correct me if I am wrong.