I want to make an outdoor billboard with a length of 19 m and a width of 6.2 m. How to set it with AI?

First of all, you have to understand a problem. Ai is vector software, which means that the picture it produces will not be affected no matter how big it is (except when there are pixel pictures in the ai file). In this case, you build a picture with the size of 190 * 62(mm), and pay attention to the exported size of 19 m *6.2 m when exporting from ps after production.