If there is any calculation to it, you could potentially create the target line with a beast mode. Otherwise you would need to add the target values to your data set and then you could use a bullet, line and grouped, symbol and grouped, etc. chart type to display it.
Case when `month`=‘Jan’ then 100
when `month`=‘Feb’ then 200
when `month`=‘Mar’ then 300
however, you should replace ‘Jan’ with whatever your dataset has