Start with the constraint
Map where change becomes unsafe, slow, or expensive. Separate technical symptoms from operational consequences and identify the workflows the business cannot pause.
Create an evidence map
Document dependencies, data owners, integration contracts, release risk, support knowledge, and the decisions that are difficult to reverse. This establishes whether the problem is local or structural.
Modernize in controlled boundaries
Prefer staged replacement, compatibility layers, and measurable transitions over a single cutover. Define reconciliation, rollback, and acceptance before moving production data.