It’s a diagnosis that is bound to make you anxious.
The best scenario is, that because they are usually very slow growing, nothing much will happen except monitoring at regular intervals. Probably every couple of months or so to begin with and then, if it’s not growing, at longer intervals.
Worse case is its removal under surgery and a recovery period. How long that is depends how big it is and where it’s situated.
In between those two is some radiotherapy to shrink the tumour to a size that doesn’t affect you.
The older you are the less likely it is to grow quickly. If it’s not affecting you at the moment (and it sounds like you didn’t even know it was there) then it may just be something you live with for the rest of your days without anything having to be done.
I hope you get your MRI soon and it relieves some of your anxiety.?