how can I delete eM client as standard mail?
I don’t understand your question. Do you need to unninstal eM Client, or set it as default or set other email client as default?
the second option use outlook as first option and EmClient als second
Then somewhere in Outlooks should be option to make that email client as default or you can make this in default programs in windows settings.
Unfortunately I can’t provide you exact place as we do not provide support for different products.