During the conversation with the teacher/school manager. The school employee may ask you some questions in English, talk about different topics to determine how well you know English .
A quick English level test can also be done using a questionnaire. In it you will see multiple choice questions where you have to choose the ones you think are correct. You will send this questionnaire for verification, the school of your choice will check it and tell you what level of language knowledge you have.
An interactive automatic test is the best and most convenient option. It is similar to the questionnaire method, but it will be checked automatically and you will know almost immediately after taking it which level group you are in you can study and what topics you have problems with.