Server manager missing

Hello, I'm coming to ask for your help today, because I have a problem with my windows server 2012 R2. I installed the trial version, and then I used DISM to change the version and switch to Standard. I activated it with a key, except that I only have the dashboard application installed, and not the server manager, which allows for example to install new features, or simply better manage the server. Do you have a solution? Thank you in advance.