The optical connection is a one way only ‘fixed’ volume connection from the TV and so the requirement here is to adjust the volume of the connected Playbar - the volume adjustment can be done via the Sonos App, or by using almost any infrared capable remote control.
Many (but not all) TV remotes have the ability to act as a ‘universal’ infrared ‘remote’ to control (connected) devices, so you need to consult the TV and/or Remote user manual, or perhaps speak with Sony support to see how to enable the universal IR remote features. In some cases, some manufacturers supply a basic remote (bluetooth capable only) but may also sell a more expensive remote that has universal IR capability, but I’m not sure if that is the case for your particular TV.
Almost any infrared/universal capable remote though should hopefully work. See these links for further information and how to get an IR capable remote working with your Sonos HT setup…
https://support.sonos.com/en-us/article/tv-remote-requirements-for-sonos-home-theater-products
https://support.sonos.com/en-us/article/check-if-you-have-an-ir-remote
https://support.sonos.com/en-us/article/tv-remote-not-detected-by-sonos
https://support.sonos.com/en-us/article/control-sonos-home-theater-with-your-tv-remote