Morgan's video is a very good one to explain everything you need to know on how that all works.
I was in your spot a few months ago and he helped me as well. Let me also add a few things.
Your bike will pull 15 Amps MAX, no matter what AC voltage you put in, that's just it's limit on the AC side.
It's just the one plug, the J1772 that whatever voltage you plug it into, goes thru, no additional plugs.
Ideally you could get yourself a 240 volt charger with a plug that fits whatever plug you have in the garage that's 240, and then put a pigtail on it so you can also plug it into a 115 receptacle as well and charge the bike. This way you can charge the bike on 115 OR 240 using the same charger and not have to get two of them.
if you have a 115 volt charger from another device and it fits, it should work. Just remember though, even though the 'charger' you get may claim to be rated at 40 amps or whatever.. the MAX the bike will ever accept from it is... 15 amps.
If you Do decide to go the 115 volt pigtail route, be warned that most of them online are NOT wired properly and will not work, even though they claim they will. I tried several and none of the 'conversion plugs' worked properly. I had to return them all
The problem is, they put the hot lead on both sides of the 115 plug, so in essence there is no return leg to complete the circuit. What they need to do is put hot on one side and the neutral on the other side It's easy to build one though. Get a female receptacle for what ever form factor your 240 plug is, (to plug your charger into), some 3 conductor wire, id recommend 12 gauge, and a male 115 volt 15 amp plug head.
Wire it together as follows.
L1 off the charger female plug goes to L on the 115 male plug (the black wire in the us),
L2 on your 250 female charger (which would be the other hot on 240 volt) goes to the N on the 115 volt side plug (N is white in us)
The L and the N on a 115 will be shaped the same, they are rectangularish.
The ground, which universally should be a green wire. goes to the round prong on the 115 volt plug.
screw it all together and when you need 240 volt charging just plug the charger in directly, when you need 115 volt, plug the charger into your pigtail,and the pigtail into the 115 volt wall socket and you are good to go.
I would also recommend making the pigtail maybe a few feet long. The 115 volt receptacles are fairly small and light weight, and having the weight of a huge honking 240 receptacle head that may be built to take up to 50 amps, may pull on the plug and cause stress / loosening issues. By having the cord a few feet long, all the heavy stuff is laying on the ground, and just the light 115 volt made for the socket plug, is really hanging off it, it's not supporting the weight of all that.
any questions please feel to ask or dm me if you don't want to ask in public
Aaron