Ross-Tech is VCDS, available from Gendan. Starts around £225 for USB dongle and lifetime updates for 3 VIN licence. You’ll need an old laptop to run it on.
When you scan the car then VCDS reads all the modules and you can clear DTC codes if present, then rescan. It the DTC fault remains (it lists priority and when it first occurred), then there’s a physical fault, mechanical or electrical and it will need resolved.
I moved away from main dealers years ago. They are £180 an hour and most of the techs these day lack the investigative nouse to diagnose and instead work from an Audi technical script or throw the parts cannon at it in the hope it resolves the issue.
First thing would be to scan the car, ensuring battery is in top condition. These cars are sensor heavy, so any drop in power will throw up an issue.
Regards parking sensors, not unusual to have a defective one. They are made by Valeo. It’s plug and play, clear faults and see if that resolves it. Normally front bumper off to fit (easier than you think). You can swap sides too. No coding as such to calibrate.
Certain components are security protected, such as certain second hand parts, MMI, ECU, etc. That needs dealer level ODIS to remove.
If you’re not particularly tech savvy you can post error codes on Ross Tech forum and wait for a response.