Configuring TI TPA6138A2 for Single-Ended PWM Inputs
You will need to look into designing filters.  The TPA6138A2 can be treated like an opamp.  

Design your filter using any method you like, and implement it using the TPA6138A2.

From the datasheet:


  Several audio DACs used today require an external low-pass filter to remove out-of-band noise. This is possible with the TPA6138A2, as it can be used like a standard OPAMP. Several filter topologies can be  implemented, both single-ended and differential. In Figure 8, a multi-feedback (MFB) topology with differential input and singleended input is shown.


Figure 8:



The datasheet recommends using TI's filter designer.

It doesn't work properly on my phone, else I'd have posted a suggested circuit for your requirements from the TI filter designer.