Remote Desktop Connection for Mac (8) - please help

Hello,

I, like many, have to connect remotely for work. I have a 2017 dell that was working fine for this until yesterday when it just shut off and now will not turn on unfortunately.

I have dug up my old 2009 Macbook and maxed out the RAM (8GB)/updated the software to the max (El Capitan). It works great. I am trying to now connect remotely to my work desktop, but it will not let me download Microsoft Remote Desktop Connection because the current version (10) requires the next level of software (Sierra) which I literally cannot upgrade to on this Mac. 

Is there any way to get access to the Microsoft Remote Desktop Connection 8? Or another way to do this? I cannot find an answer anywhere other than to ask the developer and really need to get this working. There is no way i can afford to go get another computer with everything going on. 

Thanks for your time and help!