I'm not sure if I understand you correctly, do you want to read a file from the previous day like in this example?
filename <- paste0(format(Sys.Date() - 1, "%d%m%Y"), ".xlsx")
filename
#> [1] "30032019.xlsx"
openxlsx::read.xlsx(filename)
Created on 2019-03-31 by the reprex package (v0.2.1.9000)