First, to help you, we need you to help us understand your hardware and software
- Which Raspberry Pi are you using? (All RPi3 and RPi4 have Bluetooth EXCEPT many CM4)
- How did you install HASS? Did you use a HASS OS image?
The Bluetooth integration should offer to install itself automatically with HASSOS >~8 on a RPi >=3.
Settings → Devices & Services → Bluetooth should show the integration, with likely one device (hc0 - the adapter itself). After that, it’s pretty much automatic - mine picked up neighbours AirTags, but that’s about it.
Bluetooth Low Energy support is pretty new so HASS updates are important, and as devices are often battery-powered, radio range can be a problem. Try fresh batteries next to the RPI perhaps?
If this helps, 
this post!