chart: error bars with custom error range

Hi, thanks for reading. I did a search and came up with a lot of info on this topic, but my particular problem isn't answered.

I have a chart (attached) where I'm trying to put error bars with custom values for individual datapoints, and I can't figure out how to do it except by series. I don't want the error bar on both the "pre-tx" and "post-tx" sides. I have read that I can use the "custom error bar" tool to specify a range which will populate the graph by individual data point, but I don't understand how this works. I have tried selecting the range of standard errors, but it just populates the whole series again. Can someone show me how to structure this table?

I have specified on the attachment which error I want where. Thanks.