Does the lower item rotate or push in? If it rotates, check the other front door and see if it is not connected to the shoulder belt release for the retractor. The "flipper" might be missing from it.
As @CBODY67 mentioned, the lower one allows shoulder belt to be locked to allow some slack for passenger comfort. Retractor is unlocked when door is opened and the belt is retracted immediately.
This button is integrated part of seat belt retractor assembly and I haven't found it as a separate service part. I did fix one by replacing the broken cable with piano wire and 3D printed the missing button pieces.