All sewing machines basically work the same way ….. and thus are threaded (needle and bobbin) similarly.
So, just do a Google search on …… “
how to thread a hand crank sewing machine”
Let us know how you made out.
And ps, that is a real sewing machine, ……. not a child's toy.
Homesteaders and rural households needed them in the late 1800's and early 1900's.
They are still used by people who live "remotely" off-the-grid (no electricity)