You, as the composer, need to make the final choice regarding what key you want to choose for the second section of your piece. Without knowing why you chose to start your composition in the key of D minor, it's impossible to address the mood you might be trying to create in your listeners, the feeling set up in the first section, where you might be hoping to take the music in following sections, or other considerations. What style of music are you writing - jazz, classical, blues?
There is a reason why some keys "fit together" better than other keys. Factors like relative harmonies mean that a set of sounds (like a D minor scale) will relate better with some different scales than with others. Over years of listening and composing, Western composers have discovered the relationships that sound "right" to the listening habits of European-experienced listeners. You probably are not going to discover a new combination that has never been tried before but that sounds "correct." This means you need to make a choice - either to use a standard tonal progression to reach your new key, or to do something completely different for the sake of achieving the sound you are wanting to compose.