Deactivate Simlock on HUAWEI E3531s-2?

I bought a Lte stick from Tchibo and can only use it with the Tchibo sim, but the tariffs are far too expensive. I saw that if you turn off the simlock you just have to enter a code, but where can I find the code?

The search term "huawei e3531s-2 unlock" didn't bring you Google results?

So I get a lot of hits…