Personally, I would store this data in a Dictionary. A Dictionary is used to store and re-call data which you can identify with a 'key' - a unique identifier. In this case, I would make your 'key' be the Player's name (so long as another player hasn't already used that name of course!), and in the value I would store 'SaveStateJSON'. The value 'SaveStateJSON' is only available in events called by the condition 'On save complete', and represents the snapshot of the game that is created for a save fil.
You should then use Local Storage to hold the contents of the Dictionary, so that it can be recalled at a later date. Local Storage is worth getting your head around - but I would advise reading the complete manual entry on the subject before moving forward with it. A lot of questions about LocalStorage posted on here can be fixed by actually reading the manual - it is not entirely as straightforward as it seems!