library(tidyverse)

dfa <- data.frame(a = sample(1:100,10, replace=T),
                  b = sample(0:1,10, replace=T))
dfb <- data.frame(a = sample(1:100,10, replace=T),
                  b = sample(0:1,10, replace=T))

x <- list("dfa"=dfa, "dfb"=dfb)

convert <- function(x) {
  walk2(as.list(names(x)), map(x, as_tibble), function(a, b) assign(a, b, envir = .GlobalEnv))
}

convert(x)