"设计数据库" can be translated into English as "design a database" or "database design" (depending on the context, where the former emphasizes the action of creating a database and the latter refers to the field or process of designing databases).
For example:
We need to design a database for our new project. （我们需要为我们的新项目设计一个数据库。）
Database design is a crucial step in software development. （数据库设计是软件开发中的一个关键步骤。）