From your Backoffice go to System Options and open the Auto Broker tab, check the option “conditional auto broker (from parameters)”.

Then from the Accounts Tree, go to the client or office you want and press right click and choose Parameter then edit parameter, after that in the symbols tab select auto broker if amount < from the drop down list, then edit the symbols as you desire (for the symbols you want to treat it auto select always on and for the others select always off).

Also, from that parameter you can edit symbols trading to be auto on some amounts of lots and not auto for the other amounts.
For example, if you set the value of “auto broker if amount <” for symbol Gold to 2 then that clients will be able to perform auto trading on Gold if they open position with amount < 2. Otherwise, the positions will go to chatting screen.