You start by writing down what actually hurts, in plain words, before you touch a single system or buy anything. The feeling of not knowing where to start is almost always because the problem is being looked at as one big tangle. It is not. It is a handful of specific frustrations, and once they are written down and put in order, the path is usually obvious and far smaller than it felt.
Step one: name the pain in plain terms
List the things that slow the business down or keep you up at night, in ordinary words, not technical ones. "We cannot see which customers are profitable." "Two systems disagree about the same number." "Everything depends on one person who knows how it all works." That list is the real starting point, not a piece of software.
Step two: sort by hurt, not by how interesting it is
Rank the list by what is actually costing you time, money or customers. Ignore the shiny things that are merely annoying. The most expensive problem is rarely the most technical one.
Step three: trace each one back to its cause
For each item near the top, ask why it happens. Often the fix is far smaller than the symptom suggests: two systems that need connecting, a manual process that needs tidying, a report nobody set up. Big replacements are usually the wrong first answer.
Step four: do one thing
Pick the most painful item that is also cheap to fix, and do that one. Momentum beats a grand plan you never start. One solved problem builds the confidence and the clarity to tackle the next.
If the list is long or the causes are not obvious, a short outside review gets you the whole ordered plan in a few weeks. That is exactly what a Technology Discovery and Blueprint is for.