You can choose the MS SQL database during the installation process, when it asks you for the database details, but only if the correct drivers for the MS SQL database is installed on your webserver.
Help us to help you!
Provide your LS version and where it is installed (own server, uni/employer, SaaS hosting, etc.).
Always provide a LSS file (not LSQ or LSG).
Note: I answer at this forum in my spare time, I'm not a LimeSurvey GmbH employee.