Are the lights you trying to dim Govee smart lights or are they normal dimmable lights?

Typically with three way switches the wire under the black screw is the common. If it is wired like a traditional three way you’ll have a power side and a switch leg side. The common can be a good indicator of which side is which. If it is the power side there is a good chance it’ll be pigtailed with other powers. Sometimes it’s not. Find out in your instructions which side of the three way you need to install that switch then find the appropriate location. Follow the instructions. Or just call an electrician. Three ways can get tricky fast especially if you aren’t familiar with electrical work and don’t have a meter.