If the Trackers item isn't already displayed on your dashboard, you have to add it to your dashboard under the Me section - then scroll down or tap on "3 dots" in the upper right corner and choose Select Health Data. You can choose if you want to see the trackers on My Health Screen or Dashboard.
This allows you to add several important trackers - such as A1c, LDL, HDL, and cholesterol.
MyNetDiary and PlateAI A1C tracker support manual input only; it does not estimate/generate A1C based on the logged data. It saves in historical records strictly what you enter after you get an A1C test result after a doctor's appointment. It's impossible to get an estimated A1C based on previously entered glucose amounts and then get a weekly and monthly average. The A1C test — the hemoglobin A1C or HbA1c test — is a simple blood test that measures your average blood sugar levels over the past 3 months. It's one of the commonly used tests to diagnose prediabetes and diabetes, and the primary test used to help the person manage diabetes. The measurement of the A1C cannot be substituted for estimation.
Please see this FAQ on Tracking Body Temperature for an example of how to create a custom tracker.