that is, the cord came out of the recoil starter bit....?
a general approach:
remove the cover from the side of the engine that houses the starter assembly.
it's "spring loaded" - the pre-wound coiled up spring is what pulls the cord back into the assembly - when the cord breaks or comes un-knoted the spring spins back to an unwound condition.
you have to "wind up" the spring, hold the disk where the cord goes while reattaching the cord.
depending on the exact inners / design, you may be able to stick the cord thru the hole _first_, then attach it to the rewind disk, then wind up the spring while keeping the cord out of the groove.
there's often not a lot of clearance between the housing and the disk - so your mileage may vary. some designs you have to remove the disk, wind up the spring, then re-install the disk with however it is 'hooked' to the spring.
with the cord extended all the way out, and the spring fully wound up, you then _slowly_ let it "recoil" and wind the cord around the disk.
I will caution you - if you have to remove the disk - those springs can pop out and bite. so use caution.
if the cord broke, the knot will still be on the disk - has to be removed before you can thread the end of the cord back into the disc.
if it broke, it would be wise to replace the cord as that's an indication of wear - and you'll be hopping mad if it breaks again as soon as you get it all back together.....