So, I actually had something similar one time, and the trick is, you have to know how many you need to go back to, and how it works. It’s mostly trial and error, but it can be done with Send Keys {Alt}({Tab:#}) where the # is how many times you want it to press the tab key.
now, here is a better way:
I assume at some point, the previous window(s) were in focus. So, when the window was the focused window, use ‘Get Window Attribute’. What you want is the “Handle” which may also be called the Instance. This is always specific to this window, and you should be able to define the variable. So it might be %Excel_Handle% or whatever you want to call it. Now, you can use Focus Window to go back to % Excel_Handle% and you don’t have to worry about Alt Tab messing up.
good luck!