You have specified a function called findNumber for the callback function parameter of the findIndex function. The findIndex function executes the callback function you specify once for each array index until it finds an index where the callback returns a truthy value. If the callback never returns a truthy value, then -1 is returned.
The callback function of findIndex has 3 possible arguments, with the 1st being the current element being processed in the array, the 2nd being the index of the current element being processed in the array and the 3rd being the array in which findIndex was called upon.
You are on the right track, but you need to make use of the num argument in the getIndexToIns function in conjunction with the argument in findNumber. Because they have the same name and need to be used in the same function (findNumber), I suggest changing the one in findNumber to a different name.