Create A Column Chart with tendline

Hello everyone,

I'm struggling with a chart that always semmed simple in excel, but I'm not able to achieve in Power Bi Desktop.

I've sales data (data, amount). I've created a calculated column with the month of the date. Then I plotted amount per month. This gives me a 12 column chart, where each column represents a month, and the value is the sum of amount.

Now, I want this chart to have a "linear" trendline. How do I calculate this values ? I've seen some posts on how to calculate the formula y = ax +b, but it ended up being impossible to me.

Appreciate the help,

Regards,

GV