How to insert a new column in a forest plot - meta-analysis?

Are you trying to get something like this?

label <- glue::glue("author {1:6}, {2001:2006}")
mean  <- c(1.29,0.76,2.43,1.68,1.22,1.7) 
lower <- c(0.84,0.50,1.58,1.1,0.8,1.11)
upper <- c(1.95,1.16,3.67,2.54,1.85,2.56)

df <- data.frame(label, mean, lower, upper)

# reverses the factor level ordering for labels after coord_flip()
df$label <- factor(df$label, levels=rev(df$label))

fp <- ggplot(data=df, aes(x=label, y=mean, ymin=lower, ymax=upper)) +
  geom_pointrange() + 
  geom_hline(yintercept=1, lty=2) +  # add a dotted line at x=1 after flip
  coord_flip() +  # flip coordinates (puts labels on y axis)
  xlab("Label") + ylab("Mean (95% CI)") +
  theme_bw()  # use a white background

Created on 2019-03-21 by the reprex package (v0.2.1)

If so, can you put example of your data into the reprex I've posted?
In general, it's much more helpful if you can provide a reprex, since this way we'll solve your problem much more easily. Here is more info here - FAQ: What's a reproducible example (`reprex`) and how do I create one?