how to make a variable change value within an if statement in R

I have a dataframe g with stock data with dates and price numbers. When I want Date1 to exist, Within the if statement, g doesn't become the dates specified. Here is the basic code:

Date1 <- "2020-10-31"
Date2 <- "2020-11-09"

if (exists(Date1)) {
  g <- window(g,start=Date1,end=Date2)
}

g

I don't want to attach dput, but I do want to know how to get g to equal something else in an if statement.