How to update Debian 11 source.list to testing?

[Richard Forst <sterbl.ta@tutanota.com>]

I just installed Debian using netinstall image. I thought I install testing version, but apparently it's Debian 11. So now my source.list looks like below:

    deb http://deb.debian.org/debian/ bullseye main non-free contrib
    deb-src http://deb.debian.org/debian/ bullseye main non-free contrib

    deb http://security.debian.org/debian-security bullseye-security main contrib non-free
    deb-src http://security.debian.org/debian-security bullseye-security main contrib non-free

    deb http://deb.debian.org/debian/ bullseye-updates main contrib non-free
    deb-src http://deb.debian.org/debian/ bullseye-updates main contrib non-free

I want to switch to testing version. In the past I just change the keyword from e.g. bullseye to testing, and generally there is no weird problem. But I read on the internet saying that the source.list should not mix up with different version. For instance, Debian 11 with testing. So I am wondering if there is a better way to switch to testing? Or reinstalling is the only way to go?

Thanks