Q: Can't log in Appstore on Yosemite

Hello!

I just recovered my MacBookAir with Internet Recovery. Now i wanted to install the New Beta of Sierra (or El Capitan) from Yosemite

and I can't log in for some reason...

I have Two factor authentication activated

If I login in Appstore it says that i need to take the code from another device. This works with my iPhone but I can't finde the Place where I need to type the code...

I don't know what to do.

Thank you for every help!