Welcome to the Bunnings Workshop community @oxana. It's wonderful that you've joined us, and many thanks for your questions about suitable soil types for camellias.
You might like to start by mixing in some Richgro 15kg Natural Gypsum Clay Breaker or applying Multicrop 2.8L Groundbreaker Hose-On Soil Treatment And Clay Breaker. You can reduce the soil's current PH to around 6 - 6.5 with Manutec 1.5kg Sulphur Fine Granules. Compost will also assist in improving the soil.
If the soil is really rubbish or there is a solid clay layer, you might look to replace it. I'd recommend concentrating on a 60 x 60cm section and working more on the depth. If you can dig out to around 60cm deep, that would give the plant plenty of room to establish roots. Scotts Osmocote 25L Garden Soil Premium Planting Mix would be a good replacement mix, but I'd still encourage you to mix in some compost.
Please let me know if you have any questions or need further assistance.
Oh Great! Thank you! 😃 60 cm depth I can definitely do that. What about cow manure? Do you think I can add it as well, or it will be too much?