AirPods Max not detected as my device

A few months back, I bought a second-hand pair of AirPods Max from CeX (UK second-hand seller for various tech) and had been unable to activate the device as part of my ecosystem of devices, namely, being unable to receive notifications or select marked as lost on the Find My app.

I believe the previous owner did not remove this device from their device list prior to trading it in and so that functionality is locked away after buying the headset.