What post hoc test to use after Fisher's exact test?

Question

I performed Fisher's exact test on a 4*2 table in SPSS, and I got a significant difference (P= 0.010) and I wonder what is the post hoc test to use following that? is it the adjusted standardized residuals? and if I want to calculate the P value from the adjusted standardized residuals, what degree of freedom to use?
To my knowledge, the degree of freedom is calculated as follows: (rows number - 1) multiplied by (columns number - 1), which means in this example a df= 3, however, most examples I found on the internet uses a df= 1 regardless the number of rows and columns. Thanks in advance for any help.