There’s no way to use your Sonos Ones as a front right/left in a home theater setup.  What the reseller recommended was a (poor) workaround in which you buy a very expensive Amp, not use the Amp’s main purpose which is powering passive speakers, and instead use it to group with your Ones in order to play the TV source on the Ones.  Unfortunately,  this workaround has a couple problems.  One, grouped speakers are always delayed when playing a TV source, so the sound is not going to be synced with the video.  Two, the volume on the grouped speakers cannot be controlled with the TV volume.

In short, you got some bad advice.  You can try using the Ones grouped with the Amp as suggested, but I predict it will not be fit to the task.  Consider returning the Amp, getting a Sonos soundbar instead, and either relocate your Ones as surrounds, or leave them there for just music sources.