R: Checking dataframe value in "if" statement

I need to fix a mistake in how data was entered in a column, so I wrote a set of "if" statements in a while loop to fix it. But the equal sign in if(df1[n,2] = 1) causes an error. What do I need to change?

while(n<=424){
    if(df1[n,2] = 1){
        df1[n+1,2] <- df1[1,2]
        df1[n+2,2] <- df1[1,2]
        n <- n+3