Yes, they most certainly can, and in some situations do exactly that. When that happens, you will generally receive a letter in the mail that explains what the IRS changed on your tax return, and why. Included in that letter will be instructions on what to do if you do not agree with what the IRS changed. There's usually a time limit specified in that letter for your to respond with your disagreement. If you don't respond by the specified deadline, then that's it. There's nothing you can do.
Generally, the letter will come 3-4 weeks after the return has been processed. But with what's going on in the world today there's absolutely no telling how long it will take the IRS to actually complete the processing.
Bottom line is, there's nothing for you to do until you get that letter. But you can keep checking the IRS website for the status of your return. I also think (not sure) a number is provided you can call after it has been so many days since processing started. (I think it's 60 days, but not sure on that.)
