What to do if filament spool won't fit in 3D printer
A spool does not need to be inside a printer. Or on. Or even next to.
My Ender 3 pulls his filament in from the rack above it, my TronXY X1 pulls it from about 80 cm to the left of it, where it hangs from a shelf.
When making a solution that pulls in filament from afar, it is necessary to make sure the path is unobstructed and works for the whole movement range of the printer without getting bent sharply, as that can snap or kink the filament.
In the case of the small printer you have, leave open or remove the door to the filament chamber and make sure to place the spool holder so it drags in the filament straight. There are even spool holders designed specifically for this printer.
There are many designs of spool holders out there, many of them free and with minimal assembly.
RE-spooling
Some printers, especially ones that only take marked rolls, might need their spool cores re-filled. In that case, you need to take utmost care: re-filling a spool needs to be without any twist to the filament or you risk entangling, and you need to make sure to not kink or bend the filament in doing so, or risk breaking at those spots.
Due to the risks involved, this should be avoided whenever possible!