Understanding Entity migrations

Taking the Angular x Dotnet Core course, and every time I want to start up the database, I run

sudo docker run -e 'ACCEPT_EULA=Y' -e 'SA_PASSWORD=MyComplexPassword!234' -p 1433:1433 -d microsoft/mssql-server-linux

and then

dotnet ef database update

Problem is, changes to the DB that aren’t in the migrations folder get discarded. For example, if I make an HTTP post request on the client that updates the database (say, change the price of a car), the database will properly update, but when I run the two aforementioned commands the next day, those changes are gone. What am I missing?