I would like to connect a Sonoff SV to my gate opener and I can’t find a suitable step-down voltage regulator. Input voltage will be 230v and output needs to be 5-24v. FYI I’m very new when it comes to electrical work and am unsure how I would even connect the voltage regulator to the gate opener so any tips there would also be appreciated. Thanks 
If you mean 230v AC, just get any switchmode supply and plug it into a GPO. If you don’t have a PowerPoint to plug it in to don’t try and wire it in yourself, call an electrician.
You won’t connect the gate opener to the voltage regulator. The regulator is required to provide power to the Sonoff module - just wire the output of any 5v to 24v plugpack to the inputs on the board, taking care to match positive to positive and negative to negative. If you use a 5v plugpack leave the jumper in place - if you use a higher voltage plugpack then remove the jumper.
If your question is actually about connecting the Sonoff module to the gate opener then that will depend on what the opener needs in order to activate the opening mechanism.
