You can check with the dealer (remote start key FOBs cost around $250 each) - but unless your Explorer had the remote start module, just a key FOB will not get you remote start.
Depending on the model and age of your vehicle (you really didn't give us anything to go on in your post) - you may be able to have your Ford Dealer add a remote start module and FOB.
Lots of aftermarket remote start kits around too (usually installed by audio and/or alarm shops).
I think any path will cost $$$ - but start with the dealer, they can give you a quick answer on what is needed and how much it would cost for the OEM solution (if there is one).
Remote starting is nice, but I personally wouldn't pay lots of money for it. I use it occasionally on our 2018 Platinum Explorer - mostly when it has been sitting in the hot Las Vegas sun for a couple of hours - nice to get the cooling started while walking through the parking lot.
If you have Sync 3 - you may be able to remote start from the Ford app.
You can buy the key with the extra button, program it in, then use Forscan app (windows OS version on a windows PC/tablet/etc needed to program, IIRC) to toggle on the remote start feature. A google search for Forscan remote start will provide more info.
On model years that have remote start built in, that module is not separate and is just a matter of toggling it on in the firmware. There is no need to get a dealer involved and they may not even be allowed to facilitate toggling on a feature that was not ordered to come on the vehicle.
i was disappointed my 2015 XLT did not have remote start. Researched the oem kit and was $250.00+, more than i wanted to spend. After looking at the contents of the kit, i realized it consisted of 2 5-button keys and required trip to dealer to “install” and program key fob.
I read that majority of 5th generation Exploder’s had remote start hardware already installed. I read that you needed to enable remote start, using ForScan to change 2 variables, enable remote options to show up on dash, i already had ForScan and elm27 adapter, do i did the programming. I ordered a 5-button key fob off ebay for $49.99 and waited patiently for it to arrive. Got the key cut from local locksmith for a couple of bucks and programmed it. Got out and used fob to lock up. Pushed the lock button once then the remote button twice and she started right up. Costed me less than $100.00 (if you add key, cutting, elm27 adapter and extended license for ForScan). Since then. I ordered a second key, now i have 2 working 5-button keys and the 2 4-button key I previously had. Great option for the price.