How do I choose different runners?

I’m confused about how gitlab-ci works, specifically the runners. I’ve created a .gitlab-ci.yml file in my project, and you can see here that it is working and compiling without errors

My “problem” (or I guess confusion) is that the deploy stage creates a deb package that appears to have been created on a 32-bit linux machine. I think this because when I try to install the deb on a 64-bit machine, I am given an error by aptitude that the deb is incompatible

Therefore my question is: how do I change my .gitlab-ci.yml configuration in order to compile the deb on a 64-bit machine?

For extra credit: can I also set up runners to compile my code for windows?