Buttercream icing help

Not sure what recipe you're using but I love King Arthur flour and all of their products & recipes on their site. They also have a bakers help line you can call 😍https://www.kingarthurflour.com/recipes/easy-vanilla-buttercream-frosting-recipe

I did a quick Google search and found- When frosting is too runny?It really depends what caused it to berunny in the first place. Too much milk in American Buttercream: add more powdered sugar and a little soft butter. Hot day and too soft A.B.: chill the whole bowl with the icing and the beater in the fridge.Oct 4, 2015
https://www.quora.com/Whats-the-best-way-to-thicken-runny-buttercream-icing

It’s usually too much liquid: don’t add all the milk/cream at once, add slowly as needed until it’s the right texture and consistency. If you’re coloring the icing use gel colors - they will give a better pigment and don’t add more liquid. Also, make sure your butter isn’t melting, it should be soft but not melting.
You should be able to chill it and get it to firm up some, and you can add cornstarch (about 2 tsps) rather than more sugar to help stabilize it too without adding more sweetness.
I agree with Jessica too, King Arthur Flour has great recipes!

Too soft of butter or too much milk is usually the culprit. Buttercream will melt in the heat.

Just add more powdered sugar and make sure your ingredients are not melting. You can also do half butter and half butter flavored crisco. It's what most bakeries do to prevent melting. It's not what I would do for a home dessert, but there's tricks for things done for displaying over long periods.

Thank you all, I got the right recipe and the consistency down. Now time for smoothing 😊