start with observations: x2 in class, separate subjects.
What support (reasonable adjustments) has the teacher made in class (environment, differentiation, QFT etc) Put all of these in a document.
Once you know what is going on discuss with parents, get consent -the request for CAHMS support (all therapists you feel will benefit assessment for the child), fill out EHCA with parents/teachers.
Collate ILP’s (one every half term) -make notes its a working document, you need to monitor.
Ensure the interventions are/were happening.
Once assessed submit all docs with assessment/ summary feedback and therapist interventions in place too
You can organise your diary in order of what takes longest. I would have a parent discussion and discuss local offer and what you are going to do next. Simultaneously I would fill out all forms so they can sign on the day.