The squat is a fundamental movement. If you have trouble squatting to full depth comfortably, it’s almost guaranteed that you also have trouble doing all other sorts of movements. Assuming you’ve simply lost the range of motion required and you’re not injured, there is a fairly simple (though not easy) way to regain your squat: two minutes of assisted squat every day for two months.
The equipment you’ll need is: your body and something you can grab on to that doesn’t move.
The time you’ll need is: two minutes a day for two months.
Using the thing that doesn’t move (a post, the leg of a heavy table, whatever), climb your way down to the bottom of a squat. Once there, straighten out your back. Hold the position for 30 seconds. Stand back up and go about your day. At three other times that same day, repeat the process.
Every few days, check and see how your unassisted squat feels, and if it is improving. Continue the process for two months. If the problem was that you simply weren’t using that range of motion, you will see definitive results within two months.